Hi Lilgoth, first of all RTR boats radio's are crude, thats why you cant find a crystal, also why the Transmitter has stopped working. What type of boat is this? Buying another radio system is the best bet, 2.4ghz is the way to go. Removing the old receiver and soldering new connections is only a couple of hours work, following the wiring as you have you can identify the motor and the servo connections.
Chances are that on 27mhz the original system is quite 'dirty' and would be prone to interference.
A new Tx and Rx with an ESC will not cost that much, but, would give far better control and more enjoyment for your model, plus when you want a second, it is simply a matter of swapping the parts over.
Hope this helps, post again if you want more details
Mark