That looks like dielectric grease. It gets used on cars and atvs to repel water from electrical connections.

That's clear silicone. Dirt from a pinball machine won't hurt solder. Silicone can be used to prevent accidental shorts or wire breakage. Maybe previous owner had problems with wires breaking off switches? Sure makes replacement of the switch "fun".

No.

I second TheLaw's answer! If you solder them correctly you should have no issue.

It looks like a scene from The Blob. Couldn't find humans so it attacked your pin.

It would be fun trying to resolder those if they ever come loose.

Most broken wires on my machines have been from poor WIRE STRIPPING and bad soldering. People use a knife or the wrong guage stripping tool, then poorly solder the few remaining strands anyway.

I'd never goop that crap on my machines and don't think anyone else should either.

Couldnt agree more.

That stuff works fairly well sealing gaskets on cars, but I prefer to use the "ultra black".

That isn't the first time I have seen that. When a switch gets flakey some people wiggle on the leads and get switch hits. Most of the time its a bad switch or the screws are too tight. Instead of replacing they goop it with silicone or hot glue.

Yeah, reminder of something else I'd need to look for on a machine to be purchased. I'd be asking for a couple hundred knocked off the price, just because I'd need to go through and clear and completely redo any joint done like that, and possibly replace the gooped parts. It's a sign of either really bad soldering skills on a repair (using silicon/hot glue to compensate for lack of structural integrity in a bad solder job), or an attempt to AVOID resoldering a loose connection (from lack of skill or equipment).

My recommendation for this mess? Go ahead and just replace all the switches instead of trying to degoop them. They're likely going to be cheaper than the labor, and you're probably going to have to cut and restrip the wires anyway for the best connection.