Leaky presence cap - again

[SteadyEddie]

For some reason I keep burning through presence caps.

Let me tell you what I got. It's basically a 2204 amp with a PPIMV.
Started its life as a plexi, so it has the plexi-type presence circuit with a .68 cap instead of the .1 there.

What it does is, every now and then, I start to hear some noise creep in. It starts to get worse and worse. I identified it by tapping around on the boaard with a chopstick, the presence cap sounded microphonic, so I replaced it and the noise went away ... for several months. Now it's back again.
I've used good quality caps, like Mallory M150, and a CDE DME 1KV.

Should I rewire the presence control to the newer type? What's the story with the change? I'm sure there's a reason why they switched.

[SteadyEddie]

Any ideas?

[Carbia]

Measure if you have DC on the presence pot, and tell us how much.

[SteadyEddie]

I'm not near it now but I will. I can almost guarantee that I do. It crackles and the volume of the amp fluctuates as I turn the presence knob.

[Carbia]

It's normal to have some DC on the presence pot coming from the phase inverter cathode. Usual is around 10 volts (I measured two amps some minutes ago and one has 12v and the other 9v).