When to get your amp up graded caps ???

MAC does MAC gear best. i would find out from McIntosh about the caps. After 30 years the caps probably already were replaced.
The consistent age for amp caps has been twenty years. Ten years no way.
By twenty they can use replacing. Though they could work longer. Especially if used for the whole time, and used conservatively. (not overheated, not left unplugged for years..)
You can look inside to see if they are leaking, and check the brand. Find out if they are original from MAC.

Mike at AudioClassics says the amp was checked out at the time of sale, and that if anything needed replacing, it would have been replaced at that time... So may I rest in "audio peace" thanks to all....

I don't know anything about electronics, but I've been told that some of the capacitors available now are simply better than those manufactured in the past (e.g. 20 years ago). if that is indeed the case, it would make sense to upgrade older amps' caps, although that just raises the 'how much better will the sound be for the investment?' issue. I've upgraded caps before and noticed improvement which, while not mind-blowing, was clear. if you have a tech whom you trust and will do it on the cheap, it might be a low-cost way to get better sound and possibly extend the life of your amp too.

I'm with Has2be, Wolf-Garcia and Liz.
Macs would less-likely need 'upgrade' or change for the better components which will probably be the waste of time and money.
If the time has come, you'll need to replace them with identical equivalents. To test caps(mainly DC) you'll need cap tester or DMM capable to measure capacitance in order to randomly pick up one of the crucial caps that you would like to compare to the rated values. Normally there's a lot of headroom for needed capacitance so if the DC caps loose their capacitance there's still a room to play more music before the replacement occurs. Hence you might be still OK to enjoy your amp.

I think it is sometimes necessary to "downgrade" the amp when one feels unworthy of the high quality of the sound.