Welcome to JA!
Yes it sounds like you had a gear box leak and run low on fluid .
I would have the mechanic pull the drain plug on the transmission and see how much is left in the transmission.
If it is low or no fluid left then we found your leak.
The transmission fluid should be checked every oil change,
If your paying a mechanic to do your oil change ,,, There not doing a very good job,
I looked up parts for your transmission
The rebuild kit will run about $1,200.00
A used transmission with a warranty will run about $600.00.
Labor to pull and install the transmission is 4.5 hours
Labor to rebuild the transmission is 6.4 hours
Let me know if i can help more!