it's possible that, at WOT, the movement of the engine/transmission/car can make shifting difficult. the grinding may be because the shift linkage is altered by the WOT movement and cannot engage the gear as normal.
you might be able to help the issue with
-new transmission fluid
-engine mount upgrades
-shifter upgrades
but, as jjjxlr8 said, damage of synchro's is irreversible. i hope that you haven't ground often; i think i may have ground 1 or 2 shifts since buying the car, but, in those cases, i never forced the gear. i'm sure i did a little damage but nothing that will cause the transmission to fail in the near term.
and, chrisp, calm down. your opinion of how well a person drives is ENTIRELY irrelevant to this discussion, which, if you read the original post, relates to transmission grinding and how to fix it. the OP would most likely be shifting too fast if it were his fault, and that can be driver skill but also transmission shortcomings. it doesn't seem like you've made any friends through your 26 posts on these forums, either, given what MSP2024 said.
