I have a Mk1 (I guess as its S/N is 351) but my car got stolen, so I have the unit but no sled :(
That is going to be a problem.
To the best of my knowledge, there are no spare Mark I sleds available anywhere in the known universe.
Your best bet is to hope that when the thieves strip and sell the parts of your car, they don't bother removing the empty sled and that if the remains of the car are recovered, you will be able to retrieve it.
tanstaafl.
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