So I have a non-working Gorf that got a bit toasty in some places and blew one or two of those axial Kemet 15uf 20v caps. I found an ebay seller that sells the exact same caps, so I bought a pack, but how important is it to really replace stuff like caps and resistors with the exact same component?
I've seen those caps fail before too. In this particular case, the cap's value not critical. It's a filter cap. I usually just replace 'em with a 22uf electrolytic.
If you know the application of the cap, you can change it's value significantly. For example, these caps are simply filters - to reduce the noise in the DC supply on the board. Their ratings are not critical, so you can go up in value. Similarly, in power supply filter caps, you can go up in value if you want.
Another thing you run into, especially on black and white monitors, is that there are obsolete values. 200uf and 50uf are no longer commonly manufactured - they're not part of the modern standard series of capacitor values. In this case, simply round to the nearest common value, such as 220uf or 47uf. You could even go up to 68uf. And electrolytic capacitors, at *best*, have a tolerance of +/- 10% (at least, the old ones used in video games do - I'm sure better parts exist somewhere), so they're not even exact in the first place. A capacitor marked 200uf could be really 180uf, or 220uf when new.
For bulk filters in linear power supplies, such as the Atari power bricks, and the MCR game power bricks, Williams power supplies, Midway regulator boards (Galaga, Gorf, Super Pac, etc), you can fudge the value even more, as much as 50% higher than it started as. Don't go down - the thing needs a certain amount of filtering. But going up in value here won't hurt anything.
But... if you don't understand what the cap is used for - stick to the same value, or as close as possible on obsolete values. You can always use a higher voltage rating though - provided the higher rated part fits in the space.
-Ian