Hello I will help you with your question,
Heat the area around the cap with a propane torch to remove the nylon lock and you will be able to install the new joint
NOTICE: Never clamp propeller shaft tubing In a vise. Clamping could dent or deform the tube causing an Imbalance or unsafe condition. Always clamp on one of the yokes and support the shaft horizontally. Avoid damaging the slip yoke sealing surface. Nicks may damage the bushing or cut the lip seal.
Important: If there seems to be a hang-up or binding, stop pressing, and check the needle bearings for misalignment in the bearing cup.
Once the nylon spews out like a snake you can use standard procedures to replace the joint
Please ask if you have questions
This is at the pinion yoke right? the rearmost u-joint? How many pieces are in your driveshaft?1?2?3? Is the joint #22 in this diagram?
Once you remove the retainers on the pinion yoke the shaft is on the floor and you can melt the nylon on the driveshaft yoke to release the caps of the joint then you should be able to place a large socket on the floor to support the yoke and drive the cap out into the socket. The new caps are held in with external snaprings.
If none of this makes sense maybe you can post a picture of the area you have a question about. I am not sure that I understand that you cannot see the cap?
Ok I will be here until about the time you get back or a little later then I will be on tomorrow at 8:00AM. I will try to get you a clearer drawing of what I am saying