My manual '96 Toyota Corolla sometimes is very hard to shift after I have sat at a light for a while. I have to turn the car off and put it into gear and then shift it. I took it to a repair shop and they said they drove it around and that it was shifting fine. They didn't seem to want to look into it anymore than that. What could be the cause? It's getting too hot? The engine is not overheating.

Low on gear oil The longer you drive the harder it is to shift if yes it sounds like it is low on gear oil 85 - 95 w gear oil have you seen oil spots under the front of your car ever the loss of oil could be from a bad axle seal if so do both axles

Could be a clutch problem also, especially if you have a habit of keeping it in gear and the clutch pushed in at a light. I am not disagreeing with browndene, that is very possible.Owners manual calls for 75W90 If you live where it is very cold, try 50W75 But the clutch is not adjustable, it's hydraulic and unlike many cars it has it's own master cylinder, separate from the brakes. Check the fluid, its the same DOT3 as brakes

Thank you kindly for your answers I will take it somewhere else and give them this info.