I would suggest you re-solder those two resistors - making sure that the leads have not corroded to any degree. Ideally, replace them and clean the solder traces. I use an electric eraser for this purpose.

https://www.artsuppliesonline.com/prodimg/6150.jpg

With a very soft insert. Wonderful devices that do not 'pull' traces or leave conductive scarf.

I expect your problem is thermal - and due to vibrations when hot. So, get the thing going, and using a wooden stick - something like a drumstick, tap the various components and see where you get a reaction. Clean that up, and you will be fine.

Peter Wieck
Melrose Park, PA