I did a trip to London 2 days ago and I lost 4gear in that it wouldn't engage and just slipped out. then 3rd gear started doing the same. we managed to get home but now when I engage the 3rd and 4th gear they sound really bad like really noisey and grinding. I can engage 3 if I hold it in place but the minute its not under load it slips again. Any idea what has happened exactly and what potential cost it will be to get it fixed ? much appreciate any advise on this. Obviously I'm thinking its going to be expensive and it will need new transmission but that's just me guessing.