Hi Dre,
I would take a scope and look at the voltages again and see if the left side has some garbage "AC" on it? It could be a bad cap not filtering out the garbage. Your voltages seem okay. If there was excessive current draw on the left side the voltage reading would reflect that. ( E = I*R ) If everything is clean on both sides maybe you could try a U.S. 6C4 military tube. It should be a little more rugged. Ask CJ to make sure it's okay to use them first. Three months is took fast for any preamp tube to go bad. Being that's it's always the left side something fishy.
I would take a scope and look at the voltages again and see if the left side has some garbage "AC" on it? It could be a bad cap not filtering out the garbage. Your voltages seem okay. If there was excessive current draw on the left side the voltage reading would reflect that. ( E = I*R ) If everything is clean on both sides maybe you could try a U.S. 6C4 military tube. It should be a little more rugged. Ask CJ to make sure it's okay to use them first. Three months is took fast for any preamp tube to go bad. Being that's it's always the left side something fishy.