1997 5.7L Merc. has a sealed engine coupler and Perm-a-Lube U joints. A Merc. parts man told me his shop routinely replaces these U joints with ones that have grease fittings. What's your take on this? How reliable are these Perm-a-Lube U joints? If they aren't broke, why replace them? How often should the O/D be pulled just for a look inside? I have F/W cooling, a belt driven sea water pump with a thru hull intake. Every year I change the O/D oil, lube the prop splines, the 3 O/D fittings and the drive shaft fitting. The eng. has 200 hrs. on it. Boat is operated in brackish water (very little salt) and it stays on a lift.