Supposedly rusted gear cover???

Hello I’m quite new here and have been driving my old Swede for 6 years now. V40 2.0 Bj 96, benziner. Tüv I had last in mai, and then after a totally senseless handbrake repair I got through without defects. Only because of the not completely loosening handbrake I failed for years and after the new brake saddle etc. it is now still from time to time… Will I then in 2 years at the next Tüv be in need… But my problem is another: So when I had my winter bikes put on in another workshop two weeks ago, the car mechanic told me that my gear cover would have rusted through… It was also around the gear, at the place he showed me some oil, oil puddles or stains but still none found in my parking lot? And I think that the old cover still has to be rusted through yet the Tüv I have seen it and told myself, which rusts not in a few months? Couldn’t it be the same thing to me as the girl?