This post is a retro post on a retro topic – a repair I did in 2017 on a monitor made in 1991. I got a question about (probably) the same problem in another venue and realized I never put it online. I managed to dig up my pictures and notes, so there is useful information to be shared.
The end of my (2016) post about Recapping my Macintosh LC I discovered that my matching Apple 12″ Macintosh RGB Monitor ( M1296 ) was going pear-shaped, and speculated that I’d need to recap it.
The bottom screws are awkwardly recessed. 
There are slightly obnoxious clips to pop around the edge. 
Yup, It’s a compact CRT full of high voltage parts.
About a year later, I got around to fixing it. Unlike the LC itself, the M1296 is distinctly not designed to be easy or tool-less to service (that’s fair, it’s a CRT). It has some awkwardly recessed screws, clips around the opening edge, and un-keyed connectors that make it challenging to work on. I found a couple tips on the Internet (one from techknight who had the same problem plus some cascading damage and posted video of their diagnosis/repair) that the most likely culprit was a 2200μF 6.3v electrolytic at C418 on the main board, and ordered some 2200μF 10V caps to replace it ahead of time.
Suitable replacement. Same value, >= voltage, similar package size. 
The original C418 looking innocuous from the top. 
Damage from the capacitor leak on the back. 
Most of the capacitor sludge cleaned up, slight harm to the solder mask.
Those tips were good, there was a pool of capacitor goo around C418 and no other visible damage. I removed the remains of the original cap, cleaned the board out out as best I could with Isopropyl alcohol, and put in one of my replacements, and it has been working fine since.
New capacitor installed, legs not yet clipped. The PCB has a little damage, but the worst of it cleaned up. 
New capacitor nestled into place. 
All good!
I found a 2019 post from JBRetro with a full Re-Cap list for the M1296, and they had the same known bad capacitor, so it seems to be a repeatable weak point.
