After you see it done, you'll still be wondering why it costs so much - except for the cost of the oil itself (~$50/change).
Other than the oil (which you can get for a good price at Wal-Mart, AutoPalace, etc.), there is little cost for the parts - even at a dealership. The filter and seal ran me under $20 at Pass & Weisz in Burlington. As a result, I think a group buy would be more a complication than a benefit.
If we have just a couple of cars, we may be able to do the actual work on each at the "Clinic". More than that and we may run out of space and time... my garage facilities are limited
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Even if we can't do the actual work on all of them, you'll have a good idea of what you'll otherwise be doing or getting done - and if nothing else, you'll have a chance to see what the underside of your favorite car looks like up close.