B) Great discussion...I sold my 1997 Malibu Eschelon in 2013 with 2900 hours...running as strong as the day I bought it, (Merc Black Scorpion 315HP fuel injection.) We left the engine running when we changed skiers, for the first 10 years we had it, (it was a promo boat.) I changed the oil most of the time with synthetic oil (50 hours), and it came out clean (not black.) The only issues we had was with electrical type things (engine hour meter module.) We did use the boat for kids skiing and trick/swivel for at least 2/3 of the pulls. Only really course skied with it the last couple of years.
We replaced the boat only to get a smaller wake and zero off control.
My ski friend (80 years old,) had better luck with his 1972 Mastercraft....31 years original engine and transmission!) His hour meter went out after 3 times around! It also was a promo boat from Tommy Bartlett's....His engine was the Ford Windsor 351 and mine was the Chevy 5.7L.
I wonder if SKIDIM or another engine re-builder house can chime in.