Finally getting around to fixing the trans leak I have had for near on 8 years... (under carriage is indescribly grimy) I have determined two causes:

1. My speedometer cable housing was split where it ran near the trans crossmember and apparently (unknown to me) the cable is lubed by trans fluid? Anyhow, a major source of trans leaking. Ordered replacement.
2. My Tailshaft extension housing bushing (slip yoke bushing) is plenty worn... initially I just though it was the tailshaft seal. Wrong... Apparently there's a soft metal bushing in there that over time gets hogged out by the slip yoke.

My question is: How much of a PITA is it to get replaced? I have read the bushing needs to be drilled out and a replacement pressed in?
Easier to replace the whole extension housing? Mine is the 4" housing and aftermarket replacements are pricy.

I don't want to invest too much on this (time or money) as a swap back to 4spd is on the to-do list and this TH400 will be out.
Anyone from the Las Vegas area know a trans shop that can handle this without a problem?

Thanks...

The tailshaft housing bushing is press in, it does not need to be machined out.

Take the housing off, remove the seal and you can drive the bushing out by carefully using a hammer and punch.

The new bushing will go in if you have a hammer and a proper size driver:
http://www.sjdiscounttools.com/otc4505.html

Use proper size driver to install seal and reinstall tailshaft housing.

Like Verle said, it's no problem to replace the bushing, just remove the driveshaft,mount and 6 bolts that attach it to the transmission. I would recommend taking the extension housing to a tranmission shop and pay them to press in the new bushing. They will probably have the correct one in stock, and also buy a gasket from them. Your speedometer is NOT supposed to be lubed by the transmission fluid. If you are getting fluid into the cable, then the inner speedometer housing seal is shot, and the plastic driven gear has probably got a groove worn into it. Take the speedometer housing with you also to the tranny shop, and have them install new seals, and a gear. You need to lube the cable seperatley with graphite, the fluid will eventually gum up and sieze the cable. If it is split, then you need to replace it anyway. There are several sources for new cables, including the GM dealer. I have been buying them most recently from my local parts store (O'rielly's), and they stock most all sizes for GM applications, and are manufactured by "Pioneer" (overseas).

Thanks for the info, folks. Yeah, I thought trans fluid in the speedo cable was wierd also... I remember lubing a speedo cable on an '80 C10 with lithium grease and it was dry as a bone when I pulled it out.
I need to start calling around to find a good trans shop here...

Again, thanks for the heads up and good info about the speedo housing!

I removed the offending parts tonight and snapped some pictures

http://i284.photobucket.com/albums/ll18/rogers98_photos/DSCF1748.jpg
http://i284.photobucket.com/albums/ll18/rogers98_photos/DSCF1749.jpg
http://i284.photobucket.com/albums/ll18/rogers98_photos/DSCF1751.jpg

Speedometer gear looks in good shape.
Bushing has wear marks... Hope this doesnt look out of the ordinary to any of you folks that have experience with this. Anyhow, It goes to the trans shop tomorrow.

Speedometer gear needs to be replaced... it was heavily grooved on the shaft.
Bushing, seal, O-rings, gear and gasket -- < $50
Will be done this afternoon.