First of all...good luck with that problem...I had the same thing happen last summer. Those covers are freeze plugs and you can knock them right out with a screw driver...dont worry about damage because you can get the plugs at any auto parts store.
It's a tricky little job getting everything put back together...as you will probably see... After going thru all of the trouble of re-building I found it did'nt help much. May be I did something wrong or there was another problem...I dont know...the "balls" of the shifter were in very good shape.
After a lot of headache and time I decided to exchange the shifter with one I found at a local bone yard that shifted fine. (Got lucky here as it was obviously recently re-built.) Cost me only $25 with the exchange.
The elves that put these things together in the first place must have been powerfull magical creatures...I wholeheartidly agree!