Tuning Need to replace a seal on my Crossman / Mac1 LD

Hi everyone,

I need to replace the following seal on my Mac1 LD.

I've attached a couple of photos. Is there an easy way to accomplish this?

Thanks much,
Dave

IMG_1437.1646871326.jpeg
IMG_1438.1646871326.jpeg

 
There are only 3 seals in that gun might as well do them all at once. The 2nd seal is in the cap. 3rd on the valve. 

You can unscrew the elevation and side screw and pull out the bolt. Theres are a few variations but all work the same. Twist left before pulling. There are two types of fittings in the tube. Plastic or metal. Plastic ones are easier to pull put, metal ones take a lot of pulling. 

https://youtu.be/Dr4mFBn21u4