Volvo penta 35-bought new splined drive on crankshaft stripped eventually miles out to sea requiring some carefully worded conversations with a friend to tow it back
mariner 40-the old two cylinder yammie one-bought new never missed a beat over 15 years and still going strong when we sold the boat on. Brilliant!
New Merc 90 four stroke 2001. Oil pump seals failed at 3 weeks old in entrance to poole with chain ferry behind on an ebbing tide, an onshore wind and a seacat approaching. I said "golly gosh" or something similar. After some "discussions" with Sowesters it was replaced and allegedly all motors recalled for a fix but I have met others with mariner/mercs 75/90 with same problem. Replacement motor developed knocking noise months later which was found to be flywheel loose!!!!! Last of the carb models it had float valve sticking problems thru lack of use but is now run by a friend and is fine- been better for being used.
Merc 50 4 stroke new in 2003 ish absolutely fine when I had it but has since had the grommet replaced between head and leg where the cooling water goes as my mechanic said when we bought it that it would eventually as they have "prostrate" problems.
Suzuki 90 four stroke 2006 ish bought new and has been faultless so far (except needed replacement trim sender unit at silly money) which is probably the kiss of death for it!