Small Dealer comes through again. Thanks for the valuable input.
My reading of available information leads me to believe that there are a number of different problems that MAY apply to any individual car.
1) some rear ends were overfilled at the factory and when brought up to full operating temps can vent fluid out the vent and appear as a leak. This overfilling puts added pressure on the seal and can contribute to its premature failure.
2) some rear end vents had problems of various sorts.
3) some seals were manufactured without springs or with springs that fail under normal operating conditions. Since the procedures I have seen say "look inside the seal for the spring" that strongly implies that some seals made it out the suppliers door without the requisite springs.
4) due to problems in the manufacturing process at the seal suppliers, some number of seals were contaminated with metal fragments that can (will?) cause them to fail prematurely.
5) some drivers who have leaking seals don't notice until the bearings go dry and fail. I can picture them wading through a couple of pounds of GO 90 on the garage floor and ignoring it.
6) procedures have been changed because even when replacing seals, lubricant can leak through them during assembly process and cause problems or appear as a failed seal when the seal has actually NOT failed. (yet?)
7) noise from a differential does not directly correlate with failure. Every M151 I ever drove had so much rear end whine at 50 mph and up that you had to shout to be heard over the freaking noise. But I never had one fail. Ever.
You may not have a leak and still have a bad seal. It just has not failed yet. In my considered opinion not having the fix applied is a crap shoot. The day after you decide NOT to do the fix, your rear end could puke its guts out on the road.
GM has to turn a profit or it will go out of business. Our warrantees and future with the Sol depends on GM staying successful and the Sol being profitable for them. (can anyone spell Corvair?) I don't want them making fixes that don't make economic sense. I for one will not complain because the dealers and the Company are making money and not spending bucks where its not required.
GM is owned by a large number of average Americans and peopled / managed by human beings who want to do good, and make the occasional mistake. Its not rocket science to see that not all dealers and GM are on the same page all the time. It is dissapointing to hear of a dealer bad mouthing GM though. It attacks confidence in the dealer and GM and in my mind is evidence of lack of professionalism on the part of the Dealer - which can easily translate into how they conduct their business.
In the final analysis, it is our individual responsibility to take care of our Sols and make sure that the work is done properly and in a timely manner.
The Sol is a special car. Its an enthusiasts car. It demands an educated, observant and thinking owner. If you want a bullet proof daily driver that you can drive and forget for 10 years, the Sol is not that car.