450c hydraulic filter housing plug

[PenderBen]

Hi all.
It's been a while since I used my '76 450c, but today I pulled it out for the season.
I thought the hydraulic level was low, so I began to add some hydraulic fluid, but quickly realized it was probably overfull. I added a couple of cups before I noticed it was actually filled above the site/gauge window (it can be hard to tell if it's under or over the level of the sight glass, if it's not in between). I didn't think much of it, since it's been over full before and tends to leak itself down.
So I was operating away, no problem, everything working fine, when suddenly the plug on to of the hydraulic reservoir blows out and there's a nice fountain of hydraulic fluid.
I shut it down, as far as I can tell it just blew the plug out of the top (I'm assuming it's there to do that, as a over-pressure relief). I can't find it anywhere, so I'll be ordering a new one (which will take a while since all the local JD dealers have closed).
Now, maybe it'll be apparent once I have a new one, but does anyone know if the plug is just pressed/hammered in from the top, or?
It's JD part number 15H604 (found under the 'LOADER MICRONIC FILTER AND RESERVOIR CAP' section on JDParts, or in the manual).
Is there a chance something else went wrong to cause this to happen? I know the return filter should be fine, I replaced it with a new one not too many hours ago.
Thanks
--ben

[PenderBen]

Okay, kinda feel dumb about this but I think I figured it out for myself, just needed to take more of it apart.
The plug is not what I was after, turned out to be the spring pin that holds it all together. It sheered off for whatever reason, the plunger (or piston) inside launched down into the hydraulic return tube, and that was all. All that failed was the pin.
Sorry to waste anyone's time, but maybe this will be helpful for someone in the future.

[digitup2]

We have that problem with the sight gauges at times and any one that has older machines will have this problem from time to time .Here is a way to see inside the sight windows when they get older /try dipping your finger in hydraulic oil and putting it on the window this will make the lens clear again and let you see inside .Sunlight and UV rays tend to etch the hell out of those old sight lenses and you can over fill the system but that may not be your problem there I am not sure the old Deere would push that plug out unless you had one heck of a lot too much oil in the system and no place for it to go under extreme pressure