Crowning glory :) 1966/67 SM 300 Crown help please..

Really appreciate some advice:

I'm just looking at this crown on this 66 300 SM that I recently purchased and it looks like the o-rings have vitrified inside the crown and somebody has used Mobius oil (or similar) to rehydrate it 🙁

I suspect this is a service crown, it looks like one but I'm not 100% certain?

If it's not a service crown then perhaps I could do a gasket repair, but if it is a service crown then I have no qualms about buying a new one.

In terms of changing it, are there any special procedures that I need to carry out or is it pretty much the same as a more normal crown? As I've changed a number of these using a pin-vice and a bit of heat to loosen if necessary.. If there are any videos or instruction guides that somebody could recommend, that would be great!

In addition to this, when I gave the watch a fairly deep clean I noticed a small quite neat numeral inscription (135) by the right-hand side of the crown, it's a mystery to me but, any idea what this could be or what it might refer to?

I'm attaching a few images:

Brilliant! I thought as much.. thanks for your help!

Do you have any idea what the 135 refers to? Actually, it could be 13.5

Yeah, I can't find anything similar but it must mean something related to the Watch.. And it's done with a degree of confidence so I'd imagine it's a watchmaker or somebody who is marking them in series..

By the way thank you for the link.. But I'm just going to buy a new one I don't think it's worth the trouble for a service crown.. Do you know if these were glued in any way, like thread glue or something similar? And would my best bet be to put the stem inside a pin-vice and gently apply the torque?

Really helpful thank you! Do you think something like GS Hypo cement would be best, or should I use something like Loctite 2701 thread-lock (I have both)?