The red one is for a manual and the grey one is for an automatic, those are not interchangeable. Check lmr.com they have charts for figuring out what you need. Double check what gears you have, rear gear ratio dictates which color you need,
(tooth count) also the are two different gears on the output shaft 7 and 8 teeth gears I believe. Pull sensor and shine light into hole make sure the teeth aren't stripped on it or that it is still locked in place. Just has a spring clip holding it to the output shaft and you may have damaged it by shoving the auto gear in place. It isn't very tough to change though if you did. Jack the back of the car up so all the trans fluid is towards the front and you would lose but a few drops.. four bolt on the drive shaft and four on the tail shaft cover. I don't remember there being a gasket, black RTV I believe. Might as well change the rear seal while the drive shaft is out. Cheap and easy and will most likely start leaking after you get it all back together..... if you don't. Made that stupid mistake once with a rear main seal after a clutch/flywheel change. Luckily drag radials made short work of the clutch disc and I got it on the next clutch swap. Nothing to it. You can also chuck up the speedo cable in a cordless drill and zip tie the trigger to make sure your cable is good. Just put some elect. tape around square end to protect it. Don't get crazy....