re capping

Everything looks good and the amp sounds good but it's a 1987 and I don't know the history on it. I have a Chinese ESR meter and a regular capacitance meter and so far every cap I test has shown good. The amp has 4 36000uf 100volt caps that are too large to test on the meters I have. Is there any way that they can be tested easily? 

Absolutely replace your big caps. They are the one's that will do the most damage. You will also see smaller caps, in the range of 100uF to 1,000 uF electrolytics on each audio board. Those are also good candidates. Make sure to pay attention to the uF (same or slightly larger), V(same or larger) and temperature (higher = longer life) as wel. 

You are right, there are also 4 1700uf caps. After I replace those 8 caps should I stop there? There is no other sign problems and the amp works well. I am not trying to be cheap there's just a lot caps left.

doe's re-capping depend on how many hours you use your equipment. if you bought a new unit and only use it 8 hours a week. when would you know if you need re-capping?

It depends on time and temperature. If they are at low ambient temp. then most likely they will last for 50 years. If playback increases temperature they will dry out sooner, but 8 hours a week is like no use at all. I would not worry. Will you last 50 years? :)

When capacitors dry out ESR increases usually reducing bass control (wooly bass) and/or increasing audible 100/120Hz ripple. Capacitor might also get hotter because of high RMS value of charging current and increased ESR.