Never had any issue with mine and I giged them hard then... so maybe yours was a "Monday production"....I had a '99 DSL401. The board needed the solder joints redone after about 6 months. I fixed it 6-7 times while I had it.
A great deal on a DSL40C came up & the DSL401 went. I don't miss the 401 at all.
That was 1 of the issues I had with mine. The MV pot failed & red plated 2 of the tubes.Had one for a while.Bias current flowed through MV pot.
The two DSL40Cs I have are far superior although I liked the clean channel on mine
Lots of heat bridge rectifier solder issues with mine
My tech stopped speaking to me over that amp lol!