Dugsub

Hi there Scoobyland,
Has anyone had this problem? I have a 95MY WRX auto estate. Lovely car, but, the gearbox has suddenly decided that it won't stay in 3rd gear, it just revs like in neutral. Reverse, 1st and 2nd work perfectly. Gearbox oil is red as should be. We're still at the investigative stage but appreciate we may need to buy a new planetry gear set (who is best for parts?) and rebuild. However before we do would really appreciate to hear from anyone who may have had a similar problem, could it be something simple like a sticking solenoid/valve or other electrical malfunction??
We have been told that there is a history of the gearbox not being up to the job. Is there truth in this? and as a result we are also considering a manual gearbox conversion. Has anyone out there experience of converting auto to manual and if so is this a sraightforward job, (where is best for parts)?
I know there are a lot of questions here but I would appreciate any advice as i would like to get back on the road soon without too much pain on the wallet.
Cheers
Doug
d2dug@tiscali.co.uk