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.
Not sure if this will help, but perhaps there is a very small crack/break in a circuit trace or the tube socket that is open when cool and closes when warmed up. Not sure if this would cause a tube to blow but there seems to be a correlation to temperature and expansion/contraction is a common source of temperature related problems.
Could be that the "end cap" on the 1/4 watt blue Roederstein grid resistors near the socket are shorting to the circuit traces under it....those end caps have a thin paint or some type of coating on them and the paint can break down or chip away and you get a short. Generally those resistors are pulled up off the board slightly or insulated with plastic tubing if the end cap passes directly over a circuit trace but you might want to look at that.

Otherwise, I think replacing the socket with a new one is the way to go.

Sometimes the female connectors spread apart and contact becomes intermittent with the male pins on the tube. Use a jewlers screw driver to close the female connector.
Get a repair authorization from ARC and send it back to them.
Thanks to all for your responses - I'll pass them on to the local service technician - I live in Sydney, Australia, so I'm afraid sending the unit to ARC is just too expensive. Again, thanks muchly for the advice. Cheers, Rob.
im also in australia(perth) i gather you sent it to joe at audio connection ,who is now the authorised arc dealer in aussie,ceto at audio excellence was the dealer for many yearsand had very experanced techs on this stuff,but since they closed i dont know where they went.the guy who runs merlin audio in canberra is a real gun when it comes to valve,i could personally recomend him,in perth its patric chue who dose stuff for simply hi-fi,he is the no 1 man,and has worked on near all arc models, he is the best ive seen and trust him 100%,i also had a d125 and had no trouble at all,
I have seen in my days as a repairman that a tube socket will get a loose pin in it...When the amp is on the pin in the tube will get hot from the bad connection and melt the solder out of one of the pins on the tube...If you pull the tube out and look at the pins real close you will notice that one or more look like a cold solder joint...If you don't repair or replace the tube socket it will happen again and again......Not good
Thanks for the further feedback. Audio Connection have two technicians who work on the ARC gear. Between them and ARC themselves (sent them a fax and received a detailed helpful reply) it was decided that all the sockets should be replaced with ceramic gold-pins, and I cleaned the board too. Not cheap, but problem solved.
After some deliberation, I subsequently decided to buy a Jadis Orchestra Reference - beautiful sound, no fan noise, and looks great too, but less power than the ARC combo. I had the D125 for years and soundwise couldn't justify buying the VT100 - the VS110 also didn't eclipse it.
Cheers, Rob.