Clank / Rattle at 60mph + u-joints without clips

Ok, I'm going to jump to the punch line:  How long will u-joints last without retaining rings? 
 
I ask because I've got a 98 2wd S-10 with 130k miles that has a loud clank / rattle sound at speeds above 60mph.  Its difficult to pinpoint the exact source of the clank but my best guess is the driveshaft area.  It also shakes heavily at high speeds.  Six mechanics and $2,000 later, the entire front end was rebuilt (all 4 ball joints, idler arm, control arm, etc) and all 4 shocks were replaced.  Absolutely no change to the clanking or vibrations though...
 
Although there's no play in the u-joints, I took the advice of a forum member and had them replaced yesterday.  Catch is, the latest mechanic never changed a u-joint with the injected plastic retaining rings.  He kept looking for new plactic pins to insert in the injection holes because he didn't realize the replacement joints have the retainers on the inside of the bearing cups.  After 5 hours, he sent me home with replacement joints that don't have any retaining clips and told me to avoid driving on the freeway.  He asked that I return on Monday so he could take the joints to an "expert" to figure out how to squeeze new plastic into those injection holes.  I didn't realize how bad it was until I got home and looked up the correct replacement procedures on the net.  I just inspected the joints and they're already half an inch out of aligment...
 
Anyone want to hazard a guess how long it will take before the entire driveshaft flys apart? 
  

HOLY CRAP!  Sorry, but he should have NEVER let you leave without installing the u-joints properly.  The original u-joints are retained by injecting nylon into an internal cavity.  The replacements use the clips and can be installed with NO problems by a competent mechanic.  It just takes a bit of forethought to clean off the areas where the clips would rest.  If he has already pressed in the new cups, you'll likely have to replace everything again to get it right.

Is this only the front drive shaft or is it the rear?  I'm suspecting the front as the front end was rebuilt trying to solve the problem.  If it is the front, it is not turning unless you are in 4wd.  If that is the case, then you shouldn't have any issues with it as it is.  Now if it is the back drive shaft, you need to be VERY careful! 

Swartlkk, thanks for the quick reply!  I know it's hard to believe, but it's definitely the REAR drive shaft (2wd model).  All 4 cups on the rear replacement joint are missing clips and he drilled out the plastic in the injection holes on the front joint (although the front joint is still the original).  He kept saying: "you should be ok until Monday just try not to drive on the freeway."  The word "should" plus the hint of fear in his eyes left me feeling uneasy.... ;-)  so I looked up the correct replacement procedures when I got home and crawled under to visually inspect the joints.  HOLY CRAP!!! 
 
FYI, This is a large nationwide chain (550 shops in the US).  The reason the front end was rebuilt is because the sound was hard to isolate.  I said it was probably the u-joints, but all the mechanics said no because they weren't loose (they'd grab and shake the joints to see if there was any play). 
 
What do you think?  Can u-joints go bad without being loose?  Could that result in a sporadic clunking sound (like a scredriver in a drier) + virbration at 60mph?   

Wow...  First of all, I can't believe that he would drill anything...  The method of removing the original u-joint cups is to put the assembly in a press with an attachment to press down on the cross of the u-joint while supporting the yoke and still allowing the cup to press down through.  Apply pressure to the joint, then heat the yoke.  The nylon will liquify and push out of the injection holes.  Then simply press out the cup.  Once the cup is out, flip the shaft and repeat until all of the cups are out.

I say this because drilling out the injection hole does nothing.  With the OEM setup, there is a groove on the cup and a groove in the bore in the yoke that line up when the cup is pressed in to the proper depth.  When this groove is filled with nylon, it locks the cup in place.  Without softening the nylon, you have a bear of a time at removing the old cups, with the potential of really doing some damage to the yoke.

So...  More for having the information than anything else, once you have the OEM cups removed, you need to clean up the surface where the clips go with a file to make for easier installation of the clips.  From here, you just push in the new cups, making sure to keep all of the pins in proper alignment in each of the cups.

Now, about the whole front end rebuild...  You have been severely dupped.  I don't know about the mechanics in your area, but I know for sure when a vibration is coming from in front of me or behind me.  It is relatively easy to determine.  Sounds like the mechanics you have been working with are taking the shot gun approach to fixing your vehicle at the expense of your bank account.  If I were you, I would NEVER go back to them.  In fact, I would discuss your ordeal with the local district attorney as $2000 worth of repairs that did nothing to fix the problem...  Well...  That is just plain wrong.