I made this post for another reply but it might be a help here too. These NEMA lights use a what's called a HX-NPF ballast, which is a fairly simple type of ballast as they don't use capacitors. This also means they will probably be able to last up to 50-60 years doing dusk to dawn service as long the ballast doesn't overheat.

"Any class H or 180C rated transformer varnish should work for this. I usually use MG Chemicals products as my local electronics store stocks them. No. 4228 red varnish works but it bright red in colour so if you don't like that look (works well for early Westinghouse ballasts with were red varnished) you can try something else. I think No. 4226 might work pretty well too since it's clear.

I recently re varnished a ballast using the No. 4228 red varnish and here's how it looks after.

Here's how I usually revarnish my ballasts:
1) remove ballast from luminaire.
2) sand off all loose rust and varnish from the core, be very careful not to damage the coils when doing so.
3) clean off the debris with compressed air, followed by some isopropyl alcohol.
4) run the ballast for about an hour to get the core to operating temperature.
5) disconnect power, then apply varnish by brush directly to the coil and coil. Optionally run ballast periodically to work varnish into coils.
6) let sit for around 30mins at room temperature.
7) run for 1-2 hours to allow the ballast to reach operating temperature which will help it cure faster.
8 ) if you're not in a rush you can leave it overnight before reinstalling.

Bare in mind the varnish does smell quite pungent so make sure to apply in a well ventilated area or wear respiratory protection."

This is great info. I like that 4226 is called “super corona dope”.