Distrubtor issuesvolvo

My engine is a 2002 Penta 5.7G

My engine is a 2002 Penta 5.7GI.BF.Over a year ago I had a issue where the engine would miss and run very crapy above 1500 rpms. I took it to the shop and they tested the fuel pressure and was good replaced the cap rotor wires and spark plugs and no better. Then we replaced the coil and that was the problem.
Mike
Now here is my problem now after a few trips out in the pacific ocean I have encountered a high rpm inconstcy. It feel like the motor is loosing rpm better explained moisture in the distrubtor cap. I remove the cap and there is a lot of crosion on the cap and where the rotor contacts the cap a lot of black residue. I cleaned it up while on the ocean and it seemd to fix the problem.( also removed cap and rotor when I got home and completly cleaned) Two trips later before going out i did check the cap and again there is alot of black crap on the rotor where it meets the cap. I cleaned it took it out for a trip on Saturday and it is acting up again. I have replaced the rotor and cap numerous times with the same results. Please any sugestions

"Mike, Try your best to NOT pa

"Mike, Try your best to NOT pay a shop to throw parts at your problem!
Anyone can throw enough parts at a problem, and get lucky and eventually correct the issue.
Pay them after having given you a Quote that includes fixing the problem that they have earlier diagnosed.
Not an estimate.... a Quote!

Granted, some shop time is necessary to determine the problem..... just don't fall for the parts throwing thing. THAT you can do yourself!

."

Ricardo
Thank you for your

Ricardo
Thank you for your imput. I was working driectly with the boat manifacture ( Harold Davis in Paso Robles Ca.)he was very fair with me and gave me options. I do have automotive experience. But it was back when points condensor and plugs were the basic system.
Mike