[Amps] Hunter Bandit 2000C, arcing in the tuning cap.

[Kathy Bookmiller via Amps]

About 6 weeks ago I wrote about some problems I was having resurrecting a Hunter 2000C. 
Colin Lamb came through with the shorting switch I needed, thanks again Colin. The question of what the meters were ended up being solved, It was a 1ma for plate voltage and current, and a 200mma for watt meter for anyone's future reference. 
Everything is back up and running fine, but for one last problem. As I tune up, I'm getting some arcing in the tuning capacitor at times. 
I've visually inspected it as best I can and can't see any problems, like bent parts or and differences in the spacing between plates. Obviously I don't want this to continue before I cause pitting to occur.
I'm wondering if there is still HV insulation spray available. I remember years ago having a spray can of a red insulation that I used on some big filter caps that were arching down the ceramic posts and it stopped the problem. Or should I look for some thin Teflon sheets that could be inserted somehow between plates to add that needed protection? 
Anyone have any ideas what I can do to stop this? Both loading and tuning use E F Johnson type 154-40 variables, but the problem is happening with the tuning one, not the loading one.
73,
Kathy
PS It isn't a swr problem as  it has happened even with my Cantenna dummy load.