Well, many years ago when my box had an issue and I read about capacitors being the problem, I opened my Tivo and found only one bulging, so I only bought and replaced the one. Never had another issue again. Of course now it's been retired for years, replaced by several Tivo generations. But at this point I've never try to repair a Tivo that is that old, just not worth it and probably worth more in parting it out.You don't need a capacitor tester, it's pretty obvious when they have failed by the bulging, and do them all, don't waste your efforts only doing 1 or two.
If you have basic soldering skills it's a 30 minute job and well worth doing.
If you've done the hack to the motherboard the cap replacement should be in your skill set.