Hoping someone might chime in on this prechamber deal. Per the books I have, they show a "retainer" on top of the prechamber. It is not mentioned what it really is, how it stays in place, etc. I am not sure if the glow plug needs to come out first or what? I guess I am trying to educate right now as I know this could become a mess.

Per the book, they only show "install" instruction and mention something about Orings. It's not really adding up for me. I guess my hope was this "retainer" has a seal for coolant, but all pics I find online appear to be a one part deal?

Pre combustion chambers have steel or copper seal between it and the head to seal combustion gases. The upper part is in the water jacket of the head and have a o ring to seal the top part. Not uncommon to need to put new washers seals under the chambers as edb commented overheating brings this on sometimes.

Hopefully the attachments load.  This is where I have a conflict.  I can't find anything else online to show this but per the book I have for the 75E, it shows a "retainer" with instruction to remove it as it sits on top of the precup and seals it.  I cannot see how this design can work with the glow plug in place.  It appears maybe the injector nozzle holds this down.  There is no mention in the book about the glow plug service.  

Your engine is 10 to 15 years newer than any I have so it could be quit different than I was thinking. Mine all are threaded into the head, no retainer. But Edb comment about coming loose had me thinking threaded into the head.

Early pre-com chambers are a two piece design.
Late units with glow plugs are usually a one piece design.
 

Progress. I have the injector valve and retaining bolt out. Not much fuss just yet. Book indicates injector bolt should be 105lbft so I used a 3/4" ratchet with cheater. Just took a little nudge and threaded out no biggy.

What I can see is it appears there is a recess for the glow plug on this "retainer" thing so the GP threads in directly in the pre-com. There also appears to be two thread sizes indicating indeed this is a two piece. But due to the risk involved, I think I should pull off and spot the CAT tools for this. One is a spacer, the other just a bolt, but looks like if things are even slightly off, I risk damage to the pre-com. Looks like the only thing holding the retainer at this point is Orings so I am hoping it walks out easily. I have concern there will be a conflict on the head bolt washers. It will be tight!

I am not sure of the protocol on pulling the injector nozzle but I operated carefully and put a piece of plastic bag over the injector port, then went over the top with my socket so crap could not fall into the nozzle. I then put that immediately in a plastic bag.

These are the combustion chamber tools for the two piece units.
Only the spined bolt needs to be purchased.
 

Awesome! my situation is that I have now 'opened' the machine so I need to get it done but Xmas is jamming me up. There is at least one Oring on the retainer that I cannot get a PN for. The pics in the service book clearly show 2 seals, but parts book only shows 1.

Would you happen to have specs on the 5F9072 spacer? That seems to be a pretty critical part to just slide into the chamber and the right length so the chamber threads are not damaged! CAT wants $45 for that darn thing and can't have until next week! I don't want to do anything risky but I might need to weigh some options.

I also had the idea to thread into the retainer threads, and use my small slide hammer rather than the spacer deal.  I just can't see it taking all that much to get out.  

Magnet, I replied before studying your pics better.  The "slug" you have is the sleeve or the PN I referenced.  Obviously a slight variant but......  I am curious about the slide hammer trick? 

"retainer" removed after a circus of BS. Dimensions the the slug above were nowhere near right in my application. Slug ended up being a stack of a couple sockets and a washer. And all this to find out the retainer does not even have a seal on it. I have Oring 6F8146 that is shown in the book, but it is obvious there is no place for it, and there was nothing that came out. I am left wondering what this "retainer" is even for. It doesn't seal coolant and is rather thin. Probably 1/8" thick.

I think my only play now is to jam some sort of seal in there, hope it seals, but otherwise just fire and run the machine because I don't think it is wise to potentially chase serious head drama in getting the prechamber out, and not even know if the rest of the tractor is any good.

Anyone have any experience with these "retainer" type precom setups?

What your describing for " retainer"doesn't sound familiar at all. How about some pictures!!!
Should be a shallow thread to remove the retainer that has an inner and outer seal.

Military stuff could be an odd ball as early units didn't normally have direct start/glowplug pre-chambers and later units that did were one piece.