sounds like what has just been happenin to mine, however my cars symptoms werent so bad, i didnt have loss of oil or scraping sounds, however it would sorta stall just as u described, and slighty clunky and wierdly it would run ok after warming up lol, my car is a 97 GPX, and in speakin with the mechanical engineer, whos fixing the trans, he said that the facelift 5 spd gearbox, has been known to have occasional problems, apparently the box is a similiar but smaller magna box, i have only done 80000kms so its unusal for a box to go at that stage. so at this stage im waitin to here back from him, he had a hunch it was the pump seal ??? something like that. the guy explained it that basically the pump seal wears so therfore the pressure is not being fully applied as the first gear is situated next to the pump seal housing it means the first gear will struggle but after that the other gears should work close to normal.
btw, it mite be an idea to change the trans oil, thats what my mechanic did and in doing so he found 2 small shards of metal
, if the box is gettin chewed up there will be metal shards evident when u change the oil.
im having a few issues with my 5 speed Tip box over the past week. the car is currently with a mechanic who tells me something "major" has gone wrong inside the box... the car was fine up until last week when driving back from work and I was pulling away at the lights and the car seemed to "jump" forward (almost like a stall) then began making this grinding noise at the front left, like something metal was being dragged along the road while what felt like it was getting small moments of drive then nothing but grinding noises. I pulled over and found drops of oil following me I had a look under the car and couldnt see anything apart from a fair amount of oil sitting on the bottom of the transmission so I got back in the car (now about 15 minutes later) and as I pulled away the problems seemed to be going away as the car seemed to be warming up 
I took the car for a run down some road on the way home and although there was a light noise the clunky loss of drive problem seemed to be going away??? it drove fine to the mechanics apart from reversing out of the drive where the car came to a clunky stop (still engine running) but I gave it a bit more pedal and all was well... I was told later something major has gone in the box but the mechanic doesnt want to open it up unless he has some kinda backup.... but apparantly 5 speed tips arnt too easy to come by 
so im a bit lost... the mechanic doesnt want to open up the box mainly because he doesnt want the car sitting there for six months if he cant get the parts, but he seems to be under the impression the box is completely shot but cant really tell what exactly is wrong inside... I spoke to dstocks down here and we both agreed it was a bit weird the problem seemed to go away as the car warmed up, if it was something major had blown itself to pieces as the mechanic put, you think it would be around all the time 
the planatary gears were chewed right down in some cases and like you say the 5spds are extremely hard to come by(even in japan, I was told) especially in my case for finding a complete box. but on a positive note ive managed to find some guys that are willing to do the conversion for me if I can source a manual half cut 
