Okay, here's the deal. I've got a 1995 Merc 350 Mag/EFI MP with Bravo 1 drive. This combo has been flawless for the past 8 years. Motor now has 520 hours on it. ALWAYS starts first try, even after sitting for months on end. I've done all the routine maintenance such as oil/filter changes, fuel/water separator changes, change outdrive oil etc. Anything beyond that I have a shop do it (i.e. pull the outdrive to lube the u-joints etc.)
There are some things I haven't touched. I haven't touched the spark plugs. Original plugs from the factory are still in and she doens't miss a beat. I had the original sea water pump (and impeller!) on until a week ago when it finally let go when I was putting in at Willow Beach (Lake Mohave).
I kind of figured I was due for a new seawater pump and bought a replacement pump just before the trip. During the launch I make it a point to have the hatch up and check the belts and hoses and check for copious water leaks right after the engine start. As I was pulling back up to the dock, I noticed the engine temps coming off the peg (120). I found this odd since it usually takes quite a while to warm up, esepecially in the cold waters at Willow Beach. A quick check over the back of the boat and no water was coming out the tail pipes! YIKES says me. I was only 15 ft. from the dock so I quickly shut the motor off and tied up. Temps never got above 130. Motor was only at idle for about 60-90 seconds.
An hour later I had the new pump installed and boat back in the water. The original pump impeller came out looking like it went through a blender. After I got home I pulled all the block water plugs and exhaust manifold coolant plugs and drained the water and flushed the system several times. I had one of the elbows get a little warmer than the other prior to this and I suspect some of the impeller may have lodged in a passage. Water flow and temps are all normal now.
This leads me to the exhaust manifolds. The manuals say they should be serviced (rodded out) or replaced every 200-300 hours. I've got twice that amount of time on these puppys. Should I go ahead and spring for a new set of manifolds and elbows or just "leave a sleeping dog lie"? I'd hate to pull the manifolds only to find they're in great shape and no replacement is needed. But at the same time I don't want the motor to eat water and cause a major malfunction.
If I do replace them I'd like to stick with stock Merc stuff. I can't justify the price of the after market pieces plus they don't offer any performance improvements for my SB application. After looking at the Merc parts website I noticed my particular exhaust elbow part is no longer available which is an added rub.
As a side note, I had the pleasure of meeting Mr. Barron, of Hallett fame, and several of his friends. Real nice folks. The group had 3 boats doing their annual Laughlin run. One guy had an absolutley mint 89 Hallett 270T, another a Cigarette (didn't get more details) and Mr. Barron was launching another 260 AC with a sick (in a good sense) sounding Pfaff EFI motor. Good thing I didn't have the check book cause the 260AC was apparently for sale.
Sorry for the long diatribe...