Sincro mt75 problem

[FedeMK3]

Hello everyone, I'm looking for some mechanical advice for a Ford Transit MK3. I've been experiencing some grinding when shifting from 2nd to 3rd gear for a while now. I changed the oil, using the 75w90 recommended by Ford, and the situation has improved but not resolved. The gearbox is the MT75 C8. I think the 3rd gear synchronizer is the main problem. To mitigate the problem, now every time I shift to 3rd, I wait with the clutch pressed until the shaft stops spinning while I'm in neutral, then I engage the gear and it doesn't grind anymore. Of course, I end up in 3rd at a very low engine speed, but without grinding. Do you think I can continue with this technique without any problems, or not?