Mesa dual rectifier solo problem

[Bigdrums]

This amp is reported to have the following issue: Channel 1 only- as the gain pot is turned up volume increases normally until approx 1/3, then as it is turned up past that point rapidly decreases
in volume. Past 2/3 gain on the knob begins to increase in volume but only slightly. Tubes are all Mesa brand and tested good. Gain pot removed and tested good. Also removed pot cover and looked good. Cleaned pots. Tested filter caps for value & ESR-good. Checked resistors in Ch 1 area. Noticed some transformer goo dripped out of PT, not much but a few drops. Read another post here and was talking about DC voltage present on the gain pot leg opposite ground leg. Checked and shows between 28-37 volts DC on same leg. Removed preamp tubes 1 at a time and did not change the voltage present. Note this voltage is only present with the standby switched to play or on. Otherwise the amp works fine. Schematic attached is preliminary

boogie-dualrectifier-3ch-solo-head.pdf

[The Dude]

It sounds to me like one of the caps in the tone stack is leaky, which isn't fun in that amp. I'd first temporarily unsolder the wiper of the treble pot and see if DC is still present on your gain control to verify whether it's coming from the tone stack area or elsewhere. This can be done without major disassembly. If the DC is gone, you'll have to figure out which cap is leaking and start tearing things apart.

[Bigdrums]

Dude is correct. I found the .1uf cap on the bass control measured no capacitance. This was an elongated "Orange Drop" cap. I replaced it with a similar but not the same orange drop style. Perhaps it is a "Brown Drop"? Not sure. While the symptom is greatly changed, sadly not good yet. It has a point at about 1/4 turn where it pops a little, but there volume is almost linear with some drop in gain about the same point as the pops. I'm wondering if's the replacement cap that is making the noise. There is no longer DC on the gain pot.

What would be the best type of cap in this position in the circuit? What would be acceptable? and what would not be acceptable? Obviously I need to keep the capacitance and voltage the same. 0.1uf 600v. BTW the 0.047uf for the mid control measured good and reasonable ESR. The cap for the treble is of a different type I believe.
Does anyone know what the different colored "XXX Drops" indicate? I've seen several different colors on ebay.

[The Dude]

Do the tone controls act as they should? Also, check the gain pot with a meter. Rotate the pot while metering and see if there are any jumps on the meter during the pot's rotation. A high enough voltage/current source on the pot may have damaged it. Capacitor type should make no difference and wouldn't cause this symptom- assuming the cap is good.

[Bigdrums]

Dude: right again. replaced the pot and all is well. THANK YOU VERY MUCH!