This covers renewing the universal-joints. I did not need to give the sliding section any attention on my AC.
The original universal-joints had greasing points. The AC handbook states that they should be greased every 3000 miles. Replacement UJs are available at the time of writing (2019). I found some via ebay. But these are later versions that cannot be greased after installation. If they wear out quickly, it might be an idea to drill the next set, and make greasing points?
Firstly, take photos and notes so that you can remember which way around parts go, to try and maintain the balance of the shaft. This is especially important if you dismantle the sliding section of shaft. The 2 UJs need to be aligned with each other. If you remove the paint from the shaft, you might find some markings to help with aligning on reassembly.
Instructions I've read, say that you should tap one of the UJ yokes with a soft mallet, so that one of the bearing caps will slide out. Mine required considerably more force than this! A applied penetrating oil, and then used a bearing/hub puller, which dented the bearing cap by the time it shifted. That is, I pushed the bearing cap in, so that the opposite cap popped out. Then the spider has to be pushed back the other way, to get the opposing cap out. The caps contain needle-rollers, so try to keep the spider and caps fully together, otherwise a needle-roller might slip out and get trapped. That might cause the cap to tilt enough to jam it in the yoke - as if it wasn't tight enough to start with!
The above assembly has been pressed to the left, so that the bearing cap on the left has come out. The spider has to be pressed or tapped back to the right to extract the right-hand cap. Then the spider can come out.
Installing new UJs
If your fingers have survived the above experience, then you can try and get the new UJs in. As mentioned above, the trick is not to allow any needle-rollers to fall out of place during installation. Hopefully, the grease will hold them. File off any damage in the holes in the yokes, so that the new caps get a smooth journey into place. The spider has to go into the yoke first. Then try and hold the spider in the first bearing cap as you tap it in with a soft mallet. In fact, I tapped the cap right through the hole, so that when the second cap goes on, the spider will hold all the needle rollers in place, inside both caps. Then tap that second cap, until both caps are in position. Then fit the circlips.
A fresh few coats of 2-part PU paint over epoxy-mastic, gives some protection.
It is recommended that you get the shaft dynamically balanced. Any vibration will accelerate the wear of those new bearings.