OK, so assuming that the tape you're using hasn't had its write protect tab pushed out and that you've been trying to push both buttons, then it could be that the rubber membrane these have to keep the water out has hardened and is acting against the travel of the record button? With that in mind; what happens when you press the play button slightly ahead of the record button instead of pressing both simultaneously?
If that's what's going on here, soaking the membrane in glycerine (available over the counter at your local chemist for very little cost) will almost certainly free the rubber up enough to get it supple again. The only other box I can think of which is built that way is the Hacker RPC1 and doing the glycerine soak thing worked on mine, it's been operating properly for over four year now since I did that.
Welcome to the forum, by the way.
