915 Shift Fork question

[PK Dorki]

Last year, I rebuilt my 915 transmission (1986) with the help of a friend (okay, okay - he rebuilt my transmission with my help). It had previously been rebuilt 30K miles ago by a reputable Porsche independent shop (that was about 8 years ago). Last year after the car was driven on the track by a good friend, it would not go into 1st gear (except rarely), usually grinding out when the clutch was lifted. In addition to some worn teeth (replaced), the 1-2 shift fork had slid on the gear shift rod (Illustration 301-00 in PET). We re-set it and it was fine for multiple DEs (2 drivers) and 2 race weekends. However, last weekend (July 16th), we began to have problems shifting into 3rd, with it sometimes popping out when the clutch was lifted. It would stay in if the clutch was lifted while the shifter was held in 3rd, and NEVER popped out under power once the clutch was up. We pulled the inspection plate and everything looks fine, with just fine iron "hair" on the drain plug magnet. The shift fork on the inspection cover was still sharp and tight. It did appear that the 3-4 slider (and fork) were not centered, favoring 4th gear. Tried adjusting the shifter, just in case, but no effect.

So dropped the engine yesterday, and will open the transmission case tonight, expecting to see the 3-4 shift fork slid over a bit. Hopefully, that's all that will be affected and if it is, might just relocate the fork, tighten it down, and close the case back up. If there's ANY gear damage, however, would replace damaged gears, sliders, etc. and also replace both 2nd (replace last year) and 3rd (swapped with 5th last year) synchros.

QUESTION: I've heard about aftermarket billet aluminum shift forks, which I assume will take a better bite because without the brass threads, they could be tightened more. Also considering roughing-up the area on the polished gear shift rod where the shift fork sits, so this would be less likely to happen again. Any thoughts?

PS: NO COMMENTS ABOUT BRAND OF TRANSMISSION FLUID ON THIS THREAD, PLEASE. I USE ONE OF THE TWO THAT EVERYBODY LIKES, WHICH OF COURSE MAKES IT ONE OF THE TWO THAT HALF THE PEOPLE HATE, RESPECTIVELY