Transistors are VERY hardy devices (at least silicon ones are!), if you're damaging them while soldering them in?, you most be applying the soldering iron for much, much, longer than required. It shouldn't take more than a second or two (if that?), but 10 or 20 seconds soldering shouldn't damage a silicon transistor.
Do they work at first?, then fail later?, if so it's probably not due to soldering, more likely it's exceeding it's specs in the circuit, and failing because of over heating.