[rileynp]

http://larrybiggs.net/scwf/index.php?mod=103&action=1&id=1149944477


Above contains a nice exploded diagram from cobrajet25 of the 6309 divers case. There is indeed a metal case ring and casing spring that is supposed to be in place- numbers 4 and 5 in the diagram. Sometimes a plastic case ring (or combination dial holding ring/case ring from a 6309 dress watch) is substituted during a "repair", which may or may not work depending on it's dimensions and how well it keeps the movement from moving in the case and prevents the oscillating weight from rubbing on anything.

 

[rileynp]

They are new reproductions. I've fitted 2 so far. They fit the case perfectly, but may need sanding down very slightly on the inside edge to clear the bevelled edge of the crystal. Easy job that takes a couple of minutes with a small piece of medium wet-or-dry, and ensures a perfect fit.
The original rings seem to have been cast from some kind of "monkey metal", while these repros are machined.

First, I find it hard to believe "They fit the case perfectly" when they need alterations to actually fit over the crystal Secondly, the crystal retaining rings are indeed supposed to apply downward pressure on the crystal while at the same time holding tightly to the case. Did you try using a crystal press to install the retaining rings before altering them? Have you done appropriate pressure/vacuum tests on cases with these aftermarket retaining rings to ensure they are doing their job correctly? Not going after you on the subject, but I would be careful to recommend an unproven aftermarket part that may potentially need alterations to fit in place. Hence my questions.


Oh and lastly, I see evidence of machining on original rings, why do you think they "have been cast from some kind of 'monkey metal'"? I don't argue that it is possible they were rough-cast and then machined to dimensions, but why call them "monkey metal"? Those that are cracked and rusted in my experience have obviously been ill-treated/cared for over many years.