Oh, I opened a lot of them:thmbsp:
I use GC9337 burnishing tool or just plain paper for contacts.
Then glue small magnets across contacts on the outside to mitigate the arcing - prolongs life (not mine, but relay's)
Considering tone board, I would put Silmics instead of FG at C1, C2. Silmics and Nichicon UKZ are probably the best audio path electrolytics available for us. Sometimes low leakage UKL are even better, if low leakage is requested by mfr. I have MKS2 installed there.
C7-C10 for op-amp power decoupling do not require Silmics. Originally they were 50V, I see you put there 35V, right?:scratch2: Rail is 22V. Best might be to use equal or higher voltage cap for power supplies, like UPW, UHE, UHW. Panny FM, FR. Or that same UKL.
Other suggestions: C5,C6 - 0.1uf MKP2, C11,C12 - 4700pf FKP2 or styrene (treble bleed cap - good ears will hear the difference), C 13,C14 - film (ECW, ECQ if fits, I have there MKS2), C15,C16 100pf FKP2, PFR, or styrene.
To lower noise floor resistors might be replaced with metal film such as CMF/RN. Power resistors can be replaced, too, with wire-wound or CPF higher rating.
Anyway, that still won't be enough, cause true audiophiles despise tone control
