Adcom 5400, Chinese 1998 manufactured, question on the power supply caps

Just got an Adcom 5400, Chinese manufactured 1998, and I opened it up to make sure none of the fuses was blown, and looked at the power supply caps. I see some dark brown at the edges of the caps and it's been noted in other posts that that was a mastic to hold the caps to the board but all of them are loose to light pressure. Should I assume it's the mastic? The tops of the caps are slightly convex. Should I therefore assume they're bad and leaking? No caps I've seen with suspected leakage ever turned out to be bad when I removed them. If it works ok without hum, should I assume it's just mastic goo?
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The brown gunk is often residue from some form of glue used to hold the caps in place. The plastic lids on top of these capacitors do sometimes bow ( there is a discussion somewhere on this forum where Nelson Pass references this - has to do with the wrapping applying pressure on the isolation disc and not the capacitor itself ) . I have a 5200 and a 5300 and have not changed caps in either - both measured perfectly and have been functioning as a lab amp / office amp for years now. The stock amps run fairly low bias - it is possible to improve their sound simply by increasing their bias points to a point where the heatsink temp is acceptable ( my leave on all the time and don't stress temp is 45-50 degC )