If it is working, I'd tend not to question things. You've made your fixes, everything works fine, don't give yourself headache by looking for more unless it still doesn't work.
It is very easy to go down the route of investigating a problem that no longer exists, or at least shows none of the original symptoms. It can be a huge time suck and all you end up doing is becoming very frustrated because the symptom has gone, and you're back at square one.
These machines can break just by handling the board, so the less you do of that the better. Trust me leaving it is your best option right now.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...