That sounds as if the Exchanger is not earthed.
If the exchanger is bare it could be gradually melting the case
Also if the exchanger is leaking slightly it can cause arcing around the
thermo switches, i've had these switches die whereby moisture has got into
switch and the switch has slowly burnt itself away inside, until total failure of switch.
If the switch in the middle of the exchanger goes you can bridge it out as
a short term measure, but the power will not go off until approx 120 degrees.
so if you do this be very careful of blown pipes inside the machine.
If the other one goes it will work properly bridged out, but it is not safe for any length of time as you have no backup if the other fails.
PS thermo switches can fail open or closed circuit, ie no power or full non stop power.
As far as changing vac motors go they are easy to do and will save you a lot if doing it yourself.
I always carry a spare motor, spare water pump, spare switches (Maplins)
spare pipes, fittings, hose clips, virtually anything i need to repair my Ninja
at a customers house.
I work on Sods Law principal. If i'm carrying all this i wont need it. If i leave it at home i will.