Not even close to being true. 454/502mags have better internals than 496s and they don't need anything done to the top ends until maybe 700-1000hrs.

I think its common knowledge that the 502 is the best off the shelf platform.

Another Question.

After 1000 hours of meticulous care (high quality oil, changed at good intervals) And Normal performance boat use - How much HP is lost?

As in - is a 415HP 502 still 415HP?

I think someone earlier was pretty accurate in where the motors were ran, salt or fresh water, how hard it was ran, 525's that have 70 race hours on them vs 300 hrs of typical cruising rpm's 3800-4200 for 75% of its life, and obviously meticulous maintenance. I've argued with friends when they said over servicing an engine is a waist of money. Oil changes at 25-50 hours of normal weekend use, plugs and wires annually, impeller kits every 50-75 hrs etc. all these things give the motors optimal life. Unfortunately, things do happen and parts break so I always believed in controlling the condition of the parts that were easy to maintain. We have friends that had 600-1100 hrs on Merc motors and ran them religiously. Hours don't bother me, boat condition tells you just as much.

That varies, but if its still running good with no issues, then it probably has not lost much. A leak down test will tell you a lot.