the problem would be with the electrolytic capacitors.
Therefore, I would plan on replacing all the electrolytic capacitors with like value and size capacitors. However, the number 1 priority would be the power supply caps. They are typically the easiest to get to and replace ("typically"). The problem is finding the correct value and physical sizes that will fit within the allocated space and clamps (if used) available.
There are a few manufactures out there and a few retailers that will sell the large capacitors. If you are replacing, then you really want new caps. You can find NOS unused caps, but they would be just as old as the ones you are replacing. However, they will not have been subject to the extreme heat from use. They may (read should) be connected to a variac input first to reform them slowly. But first try for new.
Also, by-the-way, you definitely do need to look at the other electrolytic caps to see if they are demonstrating problems such as leaking also.
If, after inspection of the circuit board caps and the power supply caps there is no obvious issues, then take your time in planning the cap replacement. no hurry here.
enjoy
