Bifurcated contacts are available for the single sided edge connectors - part number 08-50-0116.
The bifurcated contacts are touted to more easily conform to rough contact areas.
Do they really? Heck if I know.

If the connectors are good and you don't have an o'scope to see where it is cutting out -- freeze spray can be your best friend. When it cuts out - hit individual components with freeze spray to see who the culprit is. This doesn't always work - but sometimes it's a miracle worker when looking for bad parts.

Never tried keyboard cleaner. Just the freeze spray that's intended for this. Not sure if there are any 'added ingredients' that can short things out.

Based on your description of it slowly cutting out after being on for a while is typical of an over heating part.

Freeze mist sometimes does make a part come back to life - but only until it warms right back up again a few minutes later. But at least it gives you a place to start looking.

Another thing - heat sink parts such as the voltage regulators. The old heat sink grease tends to turn to crap after several years. Sometimes just separating the part from the heat sink, cleaning with alcohol and applying fresh heat sink compound can help.