I have a 99 RS 5 speed, 5th gear is out of it, in other words, when you shift into 5th, you get nothing but grinding. 2 main questions here, what other subies share the same transmission? And, if I can't find one, which I have not been able to yet, how difficult to repair?

Big thing is the final drive ratio. You should be able to use a tranny from other RS's and older legacies....assuming the 99 RS has 4.111 final drive ratio.

 

Without opening the case, it's hard to say what exactly broke, and if it caused other problems.

The RSs are hydraulic clutches if I remember correctly, and therefore the tranny is different then the other cable release type clutch trannies. You'll need to find tranny from a car with a hydraulic clutch, another RS or a WRX. I don't know what the gear sets costs, but if you can do it yourself, it will save you alot of money.

The RSs are hydraulic clutches if I remember correctly, and therefore the tranny is different then the other cable release type clutch trannies. You'll need to find tranny from a car with a hydraulic clutch, another RS or a WRX. I don't know what the gear sets costs, but if you can do it yourself, it will save you alot of money.

 

The RS may have a hydraulic clutch setup, but the clutch design is the same. Any push type clutch setup can be interchanged between cable & hydraulic.

Does the tranny have to come from a 2.5, or will it match up to others? And from what I can tell, the ratio is 4.11

No it doesn't have to come from a 2.5. Any 4.111 tranny with a "push" style clutch will work.