Rolex Precision 12868 crown information request

[Tritto]

G'day guys. Not to long ago I picked up a nice Denison-cased Rolex Precision circa 1968 with hand winding 1200 movement. Apart from a little degradation at the edge of the dial, it's in pretty nice condition.
Although I can live with the generic crown, I wouldn't mind picking up an appropriate signed crown. The current crown is approximately 4.5 in diameter and just over 1mm deep. It would be a non-waterproof crown designed for a case without a pendant tube. I believe the stem is likely to be 0.9mm in diameter based on standard cal 1200 stems.
I wonder if anyone here can help with a specific part number that might be appropriate and/or any likely online sources - I can fit a crown and trim a stem if necessary. Rolex probably either won't touch it or will require a full service (which may exceed the value of the watch). There are a few possibilities on eBay but it's a bit of a crap shoot - I may shell out for a crown that isn't suitable.
Thanks in anticipation.






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