This is where it can get tricky. Most manual transmission fluid is the same color as motor oil. However, sometimes manual transmissions use automatic transmission fluid. This can be confusing if you’re trying to find a leak in your manual transmission. Once again, you can use dye to help you find the source. If you put the dye in either the engine or transmission, you can then use that information to nail down which one is leaking.
To be honest, I don’t often see leaks with manual transmissions. That’s not to say they don’t leak; leaks just don’t seem to be as prevalent. Normally what I do find are the occasional axle seal leaks. For the most part, manual transmissions give me less trouble. In addition, clutches are serviceable items. This means that you need to remove the transmission periodically to service the clutch. When doing this, it’s a good idea to inspect for leaks and repair them while the transmission is removed from the vehicle. It’s also not a bad idea to inspect the engine’s rear main seal as well as the back of the cylinder block for leaks when performing a clutch service. There’s no better time to address leaks than when you have the transmission removed from the vehicle. Be sure to check your owner’s manual or service manual to find out what type of transmission fluid your transmission is supposed to take. I’ve seen countless manual transmission problems as a result of not using the correct fluid. As I said, there are a lot of different types of manual transmission fluids. Using the correct one will ensure a long and fruitful life for your manual transmission.
As with the other leaks, stop leak products are not recommended for the same reasons listed above.