Quick, get a blanket out and practice your morse smoke signals. 
I think that what is happening with these old caps is not so much an internal breakdown but more a failure of the protective casing which is allowing moisture in and killing the internals. As I mentioned, with mains sided capacitors I usually where possible go for the extra third voltage protection and fit 400v parts in a 250v environment, this due to experience.
Years ago I worked in a training centre where each classroom had a projector hanging from the ceiling. Came in one morning to find one projector that was on standby had blown it's PSU in much the same manner as the BBC PSU, and these being at the time very expensive DLP models. The boss, knowing I kept my hand in on tech, asked me to take a look and after some b***ard taking apart found that this American made projector had been fitted with caps in the mains filter network that were rated for 220v only, the manf had gone for the cheapest possible parts for the UK market. A report from me to the boss and the fire officer ensured that all projectors were pulled from the mains at the end of the day and over the year they were phased out for models that were correctly made for the UK market.
I think that what is happening with these old caps is not so much an internal breakdown but more a failure of the protective casing which is allowing moisture in and killing the internals. As I mentioned, with mains sided capacitors I usually where possible go for the extra third voltage protection and fit 400v parts in a 250v environment, this due to experience.
Years ago I worked in a training centre where each classroom had a projector hanging from the ceiling. Came in one morning to find one projector that was on standby had blown it's PSU in much the same manner as the BBC PSU, and these being at the time very expensive DLP models. The boss, knowing I kept my hand in on tech, asked me to take a look and after some b***ard taking apart found that this American made projector had been fitted with caps in the mains filter network that were rated for 220v only, the manf had gone for the cheapest possible parts for the UK market. A report from me to the boss and the fire officer ensured that all projectors were pulled from the mains at the end of the day and over the year they were phased out for models that were correctly made for the UK market.
