Audio Research D125 - help re problem

Hello. I'm having a recurring problem with the above power amp and wondered is anyone has suggestions re a cure. It has been looked at repeatedly by the local ARC dealer, but they have only a single technician for valve gear, and he has not been successful, nor very communicative.
The amp has 8 output 6550Cs. The one positioned at 'V3' on the circuit board repeatedly blows, but this only occurs during the warm up, and only in damp weather! The latter fact led to the suggestion that a film of dirt had gathered on the circuit board, and that a humid atmosphere turns this into a conductive patina; once warm, the condensation has evaporated, and there's no problem - the circuit board was cleaned, and this seemed to help for a year or so, but imperfectly, and subsequent cleans have not helped; another imperfect cure has been running a hair dryer over the valves/circuit board prior to switching it on (who said wives don't get involved in audiophilia). Needless to add, retubing several times was no remedy. The tube sockets are plastic, and clearly work well enough in other ARC amps, but I wondered if anyone thought replacing these (or at least the 'V3' one) with ceramic items would help. Any stories regarding the reliability of this amp, or similar ones, would be welcomed, and any directions towards an actual fix would be great. This has been frustrating enough to the see the amp left unused for over a year, and have me now contemplating spending a considerable sum on a new power amp - perhaps an ARC VS110 or, on a store recommendation, a Jadis Defy 7 - if anyone has horror stories re these, please let me know too! When working, the D125 sounds fantastic (I think better than a VS110) so ideally I'd like to keep it. Thanks for the interest. Rob.