+1,

I'd love to see those dyno sheets. . . . . . . .

You should be looking deeper for the cause. Mine are on their 7th season with no problems.

Hours, salt water and a bunch of other things play a part. Mine started to fail around 200 hours which is pretty common for a boat used mostly in salt water.

Yes, big difference with salt. Flexing seems to be an issue too.

All that wonderful extra ethanol kills headers faster that in that past also...

A buddy of mine had a new 39 Cigarette w 525's. His early tell tale signs of headers failing were high oil temps. The water would get past the rings and make its way into the oil filter causing it to by pass (filter & cooler) driving oil temps way up.

High oil temps were the first sign on mine and also on a friends 38TG.

Last year, I had leaks in two sets of headers; one of which cost me an engine. Looking back, I now recall my oil temps being pretty high but I was new to those motors and I thought that was the normal operating range. My current 525's rarely get above 150*, the ones in my old boat consistently ran above 200.

I've posted this already about 100 times, but the way to keep up these headers, ESPECIALLY in salt water is to flush them religiously, EVERY time you run the motor, no matter what. And I drain them once they cool down. I also pressure check them every 10-15 hours with an air compressor and a leakdown tester (ie: drain them, fill them with compressed air and see if they lose pressure).. You can do this safely with the headers attached to the engine. Don't do this with water while attached to engine because if you do have leaks, you will force water into the cylinders..

Mine too but looks like we're both in fresh water.

My headers are 9 seasons old, boat has never been in salt water, used in Wisconsin and Ohio so season is short. Consider myself lucky and keeping an eye on them.