Congratulations and thanks for the message. I have posted some information below, mixed in with your questions.

Jeff

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: It took me some time, but now I have my pair of
: plastic master time and monte carlo. I have
: a autavia and knew that I would love the
: monte carlo. But i am really amazed how
: beautifully it is made. Give me a strap and
: I will put it on my wrist...

: But now for the questions. I drive in
: historical rallyes in a Lancia Fulvia HF. I
: am building the group 4 dash as rallyed in
: the monte's in the 70-ties. I will be using
: it on multi day events. My questions: - I
: have the plastic version. How do I make sure
: the watch does not fall off its backplate.
: The locking mechanism seems to be soso.

The locking mechanisms usually seem to work well. In any case, you would see it rotate some distance before the timepiece would actually fall off. I doubt that this would happen, and have never heard of it happening.

: - Could anybody help me with one extra plastic
: backplate?

these are very difficult to find. good luck with the search, but I am not optimistic.

: - The master time is the quartz version. Not so
: nice mechanically, but keeps the perfect
: time. The bezel does not have any marks
: except one marker. Is this correct?

YES -- that is correct. Most of the Master Time bezels have only one small triangle marker.

: - My monte carlo has a 60-second bezel. Anybody
: want to swap to a decimal bezel. Or even
: better, does anybody have a decimal bezel
: for sale?

sorry -- none of these in the parts bin at the moment.

: - What does T<25mc mean?

That means that the dial has tritium (rather than radium) and that the level is below the mandated level (25 millicuries). Below is a link to an article that goes into far greater detail on the history and issues of radioactive materials in watches.