Westerbeke Generator Tune Up

What color is the smoke?
Clear up under load or smokes when loaded?
Little oil sheen?? After starting? Running cold or warmed up? Under load more sheen?
How is the crank-case oil consumption?

Sadly, those lil Mitsubishi engines don't do well with lots of hours and don't rebuild well.

Grey smoke is usually cold or low compression. Unburned fuel igniting in the exhaust.
That sheen may be more unburned fuel also.
There is a small chance a valve adjustment may help.
I fear you have a leaking exhaust valve.
My first step would be to check valve lash and determine if a valve is not closing all the way or recessed.
Another idea;
If there is enough exhaust pipe between the head and exhaust manifold and if you can get to them, shoot those exhaust pipes (at the same location) with an IR gun.
All pipes should be very hot and near the same temp between all the cylinders. The cold lung would be your first suspect area.

Keep us up on what you find.

I'm in the wrong part of the world to help on a local (to you) shop or tech.

Engine parts directly from a Mitsubishi industrial part jober is a great path for saving bux.
Sadly, not much generic or cheap for the Worst-r-break parts.

That just finished its break in cycle and starting to wear in.
A good fresh engine like this should not smoke unless it is a dock queen.