There have been 2 crowns used in that time area for the Heuer 980.020L, the bajonet style screw-in (trouble) and a normal screw-in one.
The bajonet style is signed "Heuer" and the normal screw-in one is blanco.
For more info about how they operate, see the pictures I just took from a Heuer manual and a supplemental instruction:
View attachment 299656
View attachment 299657
Why is the bajonet style trouble?
Most of them have been broken by their previous owners either due to not knowing how to operate them correctly or just bad design, and do work now as a push in crown, screwing in does not do anything to secure it, and it will surely pop out when you are not aware of it, so the watch is not waterproof at all. To repair, find a good functioning "heuer" signed crown, which is obsolete and finding a working one is a needle in the haystack so to say, or replace both crown and crowntube to the later style TAG Heuer screw-in crown. Cost around 50-100 USD, depends on watchmaker.
Succes!
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