Port engine turbo turning up slower than starboard

Check fuel filters and air filters first and your bottom/running gear is clean
Your mans have a boost sensor that occasionally goes bad and will cause that but usually it's not so subtle
After that, it's probably the turbo getting some wear in it and needing a rebuilt soon

Do you have algae in your fuel and how many times have you changed the racors in that 100 hours? A good rule of thumb is to change your secondaries every 2nd time you change your racors, maybe you could stretch it to 3x with 10 microns but it's pushing it a little. But at 100 hours I would change those. Have you done the thousand hour service? Specifically adjusted valves? Re-torqued cylinder heads at all? It could be the aftercoolers are starting to get plugged too. Have all of the heat exchangers coolers ever been cleaned specifically aftercoolers? My instant thought is turbos are getting some wear.

There's 2 rules of thumb......I manage a Sunseeker with 1100 Common Rails. I do all of the maintanence by the book (on hours) and service the motors annually even though they don't see a lot of hours. When we change the fuel filters annually they have 100 hours (or less) on them and are crystal clean (for example). But I change them anyways. BUT, we have never, not once, had any issue that inconvenienced us on a trip or anything with the motors. One issue a newly installed fuel line would suck air at cruise once and a while and drop 200 rpms briefly and pick right back up, but we got to where we were going (SC) and home (FL). We just had racors installed because the boat didn't have any primaries aside from the Man primaries and secondaries. And I once had to overnight a battery charger to GA and install it. But we then had the old one rebuilt and have in on-board as a spare so it won't happen again. BUT, the owners always have an enjoyable trip without headaches the 3 trips a year they do with the boat and it's a 2007.

OTOH, I managed a 63' Ocean SF 1987 that the same owner had from 1988 and I managed it from mid 90's to 2008 when he sold it. He did the basic maintanence like oil changes and fuel filters and stuff.......but never really maintained everything. He was very mechanical and of the fix it when it breaks mentality. He ran the boat with his wife and did 3, month long trips a year.......every trip he had to fix something that broke somewhere along the way. One example is the generator started eating an impellor every trip, this goes on for 3 trips and he puts a new waterpump on it, then it does it again. He asks me to change it, I change it then notice it has limited waterflow. I ask him if he ever had the heat exchanger cleaned, his answer was never. It had 2600 hours on it. I pulled it off and it was packed solid with broken off zincs and junk. Had it cleaned and never had an impellor issue again. A lot of that could have been avoided by maintaining it properly and did he really save much money in the end? Probably not after having to have parts overnighted to all over the place and days he lost spent in the engine room.

Ok, I'd do fuel and air filters given what you've stated, but seatrial first. Did they visually inspect the turbo's when doing the 1000 hour service? Fuel filters are typically the biggest source of performance issues by far. But you can tell that with common rails by running at cruise and looking at the gauges before doing anything. I'm going off the top of my head. Fuel pressure common rails usually run at 85PSI, but you should see anything above 70PSI. Air inlet vaccuum/pressure measurement should be less than -5 (I forget what MAN calls this on the display). Rarely but does happen the air filters get old and crush at cruise and create a restriction but you'll see this on the display with higher air inlet restrictions. It could also be a boost sensor......look at boost pressures as well between both engines. especially coming up to plane. Seatrial the boat first before throwing parts at it and record readings for both motors at 80% load, but 100 hours is a good time to change secondaries anyways. Do they reach top rated RPM's?

On the westerbeke, you should change the exhaust riser and clamp also. They usually go 1000 hours and then create a huge mess when they fail.

I think it's air inlet pressure on the mans, definately check boost as you're coming up on plane (both engines). Rpm's sound fine and are close enough at WOT. If you can access the riser, it's usually not too bad.....the exhaust hose clamps first and get that off. There is a temp sensor which is 2 phillip screws and then the once band clamp which is a 7/16 nut..and a gasket to scrape off....the hardest part is keeping the riser and gasket lined up while you tighten the band clamp. But on your boat it's on the aft side and kind of tucked under the ledge for the engine room door......It might be easiest to take off the band clamp first, then the temp sensor, then the exhaust hose. Then install temp sensor first, then band clamp, then exhaust hose.

I have not experienced what the book is telling you. I have changed the racors, then the Man primary metal filter (with the screw on clear bowl) and then the 2 pleated paper filters (secondaries) inside of the metal housings on the top rear of the motor. I know or was under the impression there was a s/s mesh filter like you're talking about which I've had cleaned by someone else. But I am not familiar with what the book is saying but that looks to be after the primary and secondary filters. That looks like it's on the injection pump itself which was the s/s metal screen I had a Man dealer clean.

Yes, if they're the pleated ones like the K+N's I do clean and oil them and use the K+N stuff to do it.

What pressures are you reading for fuel pressure, air filter, load, and boost on both engines?

Cruise RPM mainly.