HELP! prob with analog machine

["anti:clockwise" <anticlockwise@tensionheadache.org>]

yikes!
any of you who could actually recognize an open reel of tape might have an 
opinion on this one.

tascam 38 1/2" machine: deck is otherwise very clean and in good shape.
tape track 2 often - but not always - will  not return output to the 
console.
our testing kitchens have confirmed the following:

- it's not the snake
- it's not the input channel
- it does not seem to matter if noise reduction is engaged or not.
- swapping the rec/repro card with that from another track changes 
nothing, 
the problem does
         NOT migrate.
- i can see the meter moving - it just doesn't send much signal. 
occasionally i get about as much output as a bad case of crosstalk.
- some nights 2 is fine. some nights it only works for a little while. 
some 
nights, it takes the night off.
- i can't think of a single thing that's changed in the setup EXCEPT that 
the heat in my apt. came on with a vengeance this year, and it was like 
death valley in there for awhile - i have since turned the heat in that 
room off, the problem continues intermittently.

your suggestions, commiserations, prayers and special hoo-doo effects are 
roundly invited.
replies off-list are just fine.

a: