I think David also remembers the incident and has provided some detail. I was probably exactly on the hairy edge of overvolting, and definitely over current. If you search back in the TCML archives you can probably find my postings about it. It was sometime last year.
As I said, when I paralleled the 37667s I never had another problem with them in my SG coils. So maybe it was overcurrent. Somewhere I have the JTC files and I'll send them to you off list when I can dig them out.
That larger, 50kv rated cap had a very low max - rated reversal rate. Far too low for coil service. I didn't bother reading the specs when I got it on eBay for really cheap. I thought I was lucky. Ah, here's the failure pics<http://www.flickr.com/photos/iceowl/5437138473/in/photostream>