I have an airgun (springer) tuning guide that has lots of info in it and it explains some things mentioned below in more detail, so if you want it email me at chevota at hotmail. That goes for anyone...
The spring compressor is up to you but that gun is rather easy to do by hand. With the barrel removed, I simply put the aft end on the carpet and push down on the breech end using ~50lbs of my body weight, then I loosen the screw/lug then adj pressure until I can get the screw out by hand. Then slowly let the guts come out. The reverse to get it together... Many people make or buy a compressor, then once they use it they tell me it was a waste of time and $ b/c doing it by hand is so easy and faster. Depends on the person and gun of course, like the new Benj NP2 needs a compressor. I have sketches of two different spring compressors in the guide, one is very simple, the other is ultra simple and likely free if you have scrap wood around. I think mine are better and no doubt cheaper than other home made units, so no real expense or loss if you decide you don't need it again.
The oem spring is rather long so expect it to extend out maybe four inches? The spring rate is low but that length adds up so compressed pressure is maybe 60lbs? A guess since it's been so long but it was easy. The oem seal was some funky whitish material that crumbled with age, I think it started to fail after 10, maybe 15 yrs? When I replaced mine the only option was yet another oem so that started to break down too. Now I have the nice one that you're getting which seems like polyurethane? Whatever it is I imagine it's good for a lot longer. On the aft edge of the seal mine was rather sharp, meaning it would squeegee lube back aft, so I sanded that edge round to help prevent that. I mean it still will more or less but it'll surf over more lube now. Theory in my mind is it'll keep the seal and bore etc lubed longer if it's not wiping away but instead allowing some to also slip past and get in front of it
Some misc other info if you or anyone is interested:
NEVER use silicone on the piston and misc friction areas of any springer, especially nice ones, and especially the 124!!!! Reason the 124 is especially vulnerable to this poison is b/c the design puts a lot of stress on the inside of the receiver tube under the scope rail. The linkage when cocking is pushing the piston not only back, but up, so the aft end of the piston (aka skirt) is scraping on the inside of the receiver (aka compression tube). There are other areas that can suffer if silicone is used so I'd say never use it anywhere, but especially the piston and especially on the 124. Fyi the pix in my guide showing damage caused by this piston scraping is of a FWB 124...
Ideally you should button the piston which is easy and is simply putting plastic on the pistons skirt so it's a nice slippery surface rather than metal to metal. How to do buttons is in my guide. If you don't want to use buttons then I highly suggest moly or tungsten disulfide dry lube on that area, then moly paste or a home mix of grease. Either way an inspection of the tube for damage should be done and if needed (most likely) the area should be sanded. You don't want new buttons being tore up/destroyed on a damaged area, and you want that area sanded to better hold lube, especially so if you don't use buttons. I'd likely use 220-320 to get the scratches you want for lube storage, then smooth the high spots of that work with 400-600. Basically I'd use 220 & 400 if no buttons, 320 & 600 w/ buttons. If you don't use buttons then you should also grease that spot more often, which involves removing the stock to access it and it's still a pain to get in there, so better imo to make buttons. With buttons you really don't need grease, so you could let motor oil travel down the cocking linkage and ultimately end up where it needs to be. So the time spent making buttons is worth it in time saved later, but they also make cocking easier and smoother. Making a piston liner for the spring is another thing you can do which will make it smoother and quieter, so much so it'll seem like a gas spring. A liner is also free but takes some time to make, but totally worth it. An option to a piston liner is spring tar, but I would never use clear spring tar b/c I'm almost certain it's silicone. So if you do get the black stuff, and Maccari is the source. Tar is super messy and costs some power but it's very easy to use and very effective at dampening spring noise.
Fyi there are aftermarket springs for it but the rather unique and super high quality oem spring is very nice. An aftermarket will net maybe two more ftlbs energy but the exceptionally light cocking effort will go up much more than the % in power gains, and the reverse recoil will go up and accuracy down. It's ok try one, but I think the oem spring is pretty much perfect. Whatever the case, never toss the oem spring.
If you want to put a scope on it (or have issues now) you can get one of the mounts in the guide, either the two piece mounts or the one piece and maybe add a couple more screws per the guide and you won't need to worry about it sliding.
