I recently purchased a 2010 Forester with 95K miles and a manual transmission. The fourth gear would grind a bit when shifting fast, and I would have to make sure that the shifter was pulled hard all the way back to get it into gear. If I didn't the gear wouldn't engage and the gear would grind like it was sitting on top of the input shaft. I changed the fluid and it was black coming out. I put in 3 quarts Redline lightweight Shockproof and the rest Motul 300 75w-90 and it got rid of the grind. I do still have to really make sure 4th gear is engaged though. Could this be a worn shift linkage or bushing to replace that will tighten up the spacing or slack in shifting?