Glyptal is expensive because it's a proprietary product. "Liquid Electrical Tape" or "PlastiDip" would both be suitable replacements. Just make sure you clean the parts well before applying it to get any grease or oil off the parts.

I've been using the ceramic "Sand Block" type of resistors since the early 1960's, and I've seen them in 30's~40's radio gear, so they've been around quite a while. Nothing 'magic' about them, except that they used to be dirt-cheap!

- Jim