Dealership says they don't carry differential fluid, had to provide own

Yep

 

For many years my family would use a independent mechanic who built his buissnes on that exact principal.
There were times I went to see him with a basic problem, and he would tell me how to fix it and send me on my way rather than just take my money for a easy fix. His hourly rates were on the higher side, but he was so good that he worked quicker and came out to about the same as the crappy guys.
When I was playing high school sports and tried to get him to buy some sponsorship, he offered to just donate money, but didn't want the advertising as he was way to booked as it was. For the past 20 years he had not done a single advertisement. Just word of mouth kept him booked.
Unfortunately, he has gone into semi retirement and will only work on Subi's at this point.