If the shaft was not installed properly, it would not fully engage into the transmission gear where the clip holds it, so most likely it would make a grind noise or come out, causing loss of forward motion, than it may be difficult to re-install from damage to the splines in the trans.
The bearings/balls, and cage cannot be serviced separatly, the shaft will have to come out.
Even as tough as it may seem, I haven't had a shaft permanently stay in the trans, when you remove it is a different story, if the trans was damaged from a prior install, or damaged during this removal the new shaft may not go into the trans, in which case the trans will come out. In some rare cases i've had to "torch" the axle in half, than heat the joint, so that we gain access from thermal expansion and the joint will usually come out. This is for the worst case senarios, since the heat can casue further transmission failure.
Your not crazy, removing driveshafts can even be difficult for the professional, if you don't have enough work space from under the vehicle, this is your key. If your can raise the vehicle at least 2' off the ground with heavy duty jack stands, you may be able to get the prybar in there better with more levarage, or be able to get a couple of good strikes with a hammer on it.
Rip
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