How reliable is 1978 50 hp mercury outboard?

I have a 1978 Merc 500 (50 HP) and have owned it since 1987. Since then, I have replaced the water pump impeller $25 and replace/installed myself. Also, 2 years ago I removed the carbs and installed new gaskets. It was in Excellent condition when purchased and still is. It starts with a single "bump" of the starter when warm. I use it infrequently, about 10 time per year, but love it nonetheless.

A rock soild engine by Mercury. I am also meticulous about mixing oil/gas. I do it exactly.