Voltage does not make for an OK battery. It needs to be load tested too.

14 at idle is also not always OK. Voltage and amperage varies under load and RPM.

Personally, I would get the battery and the alt tested for S&Gs. I would also take a very close look at your battery cables. If the ends were gross, then there is a good chance the corrosion has worked its way under the insulation and up the strands in the cable.

I would also continue checking grounds. Stick with the big ones for now and chase the others as you find them.

Good luck. This is going to take some good old fashioned elbow grease and a basic system to take a look at everything.

Michael

PS. This thing has spark plug tube right? Are any of them full of oil?