[MERCrunner]

Not exactly sure what you are inferring...but, are you showing that the two mtg bolts for attaching the manifold are missing?

 

[MERCrunner]

You are correct...one bolt. Sorry about that. I don't know if there is a good answer as to whether you'll need a new compressor or not. If it were me and I was servicing the a/c system myself, I'd take a chance on keeping that one. If it didn't work out, all you're out is a couple cans of freon and your time. Different story if you are paying someone hundreds of dollars in labor to do the work. This is all dependent on whether the compressor clutch still turns by hand and isn't seized from loss of lubrication.