Eng Fuel Filters Man CR900

What original filters are you not using?
Did you at least use new O rings and gaskets (oiled)?

Check the crush washer on the secondary bleed screws. Did you lubricate the new gaskets with oil before installing the filter and are you sure the old gaskets came out?

Interesting. Fleetguard is good stuff. Should not be an issue.
If this is a new problem since your filter service, then there is a leak somewhere.

I know I always have to wrestle with the secondarys to get the plastic caps back on. I remember cracking a cap getting one off. On SeaRays there is not much vertical room to even reach an arm to the far filter.

If your E/R is like these, it could be easy to damage an O ring or crack a plastic cap. You may never see a fuel leak if your tanks are low.

Also, look down into the valley between the heads. You may have to remove the cover and tilt up the computer. All those tubes and hoses and pumps are down there. Your looking for a fuel puddle.

I worked on a leak in there once, never again.

I don't remember any plastic caps of any sort on MAN 900 secondaries. The Man Hummel primaries have the plastic bowl and yeah, they need a lot of torque to tighten. Also sometimes the water sensor will crack where it goes into the plastic bowl and allow air to get sucked up when the motor is running.

Are both motors airlocking or just one? If it's both, are you sure the Fleetguard filters you got are the correct ones?

I was under the impression the MAN secondaries that are in the canister, that the canister was aluminum or metal, not plastic.

Item #1 is the black plastic cap.

If I remember, this sensor is mounted on the outside of the right turbo plumbing. sticking straight out.
If on your port engine, it's a real pain in the ribs and hip when passing between the engines.
Usually the connect and real small gauge wires get damages or loose.

We made up a banjo fitting that turned the sensor 90 degrees. Saved my left hip.

BTW; ER or E/R = Engine Room.

If the connect and wires look good, swap the sensor between the engines and see where the problem goes or stays.
DanFoss Sensors fail regularly and are expensive from MAN.
Wish I could get a cross reference and buy them straight from DanFoss.

If your sure there are no other leaks, turn your tanks off, remove the tops again. Inspect for cracks around the hex pattern on the top and nicks in the O ring. If all looks good, grease up a fresh O ring and reassemble.
Your not looking for tight, but ensure the cap is all the way on; lip of cap down to filter case body.
Over torquing may cause a crack between the course threads to the lip of the cap.

The O ring makes the seal, not the cap lip. When the cap lip is just down to the filter case, the O ring is in place.

Finally had to look up Seychelles.
Sounds like a beautiful place.