200hpMerc-hole in piston-bad bore

[LDH]

Please help, I'm just a back yard mech trying to get my fishing boat working. I bought this '88 200hp Merc w/"low comp" on #5. Actually, 1 thru 6 ran 70, 95, 85, 100, 90, and 0. So I've pulled apart after having bought 2 pistons gasket set, ring set, etc. #1 cyl is scored but maybe OK. #6 (piston w/hole, 1/4 around top edge between lower transfer and exh ports) cyl is still pitted and scored through the chrome a little.
Questions--
1. thoughts on what caused this?
2. Do I need to have bored/sleeved #6?, #1?

I have some dig pics if anyone is interested.

Thanks very much in adv for help. This looks like a very sharp group!

[Georgia Boy]

but I would have them bored or replaced before i rebuilt it, if you have gone thru the trouble to take it down, i would not half ass it for this,

[LDH]

Hey!! I think I found the problem. pasting my reply to the boating newsgroup.
Well, thanks everybody. Nobody told me to go run it til it dies. I don't yet know how much it will cost but my $2,000 deal on the boat motor, trailer is getting up over 3m, I hope not over 4m. Larry, good point about the leakdown. A few years back (actually, a lot of years back), I lost three pistons on three enduros in a row (kind of a road ralley through the woods on a dirt bike). Finally, I realized the mag side crank bearing was moving. It wasn't the bearing but a cast in steel liner in the case for the bearing. The movement of the crank allowed air (and dirt) to be sucked in, leaning the mixture and giving it a good scouring. Actually ate up a set of rings in 30 miles and I ran out of gas!

NOW, I've removed the pistons, pulled the crank and guess what???? the large bottom crank ball bearing had the retainer (plastic) come apart. There's 8 balls, s/b 8 spaces but only 7 pcs of plastic fell out. Also, arould the crank counter weight adjacent to this bearing, the alum is polished. I will NOW bet money, the retainer disenegrated, a pc went in to the crank case, the crank wobbled, sucked air in through the seal yadda, yadda, yadda. (I'll still ck the carbs though).

Anyway, the good news is my labor rate is so low I might can afford to fix this thing

Lee