If it's shrunk in both dimensions, the HV diode is likely just dirty (which is a common issue on all of these). You don't need to replace the diode and throw a still-good $20 diode in the trash. Save the diode you bought for a machine that actually needs it, as 90% of the diodes in these are still good, they're just dirty. But you DO need to clean out the old grease from the boots, clean the springs, and solder the springs to the diode, which you'd still need to do regardless, even if the diode was bad. I have a detailed post on it here:
I have updated first post with some of the myths and their status. Will try to catch up and add some others but if you feel real strong about changing status of one, quote it and post a fact. The fun ones are fine but too many for me to try and update.
forums.arcade-museum.com
Other than that, just do a cap kit (as there's one cap in the HV that goes bad). The deflection board caps don't usually go bad, but you might as well replace them if you're going in there anyway. Then just reflow the headers, DeOxit all header and Molex pins, and you should be all set.