All of a sudden i been having troubles shifting into 3rd gear in high revs. I guess the gearbox is on its way out.
From experience working on trannys is it a really big job pulling it out and having a look?
A problem like mine will it it be noticable what the problem will be when i open the tranny?
Any advice would be great?

 

try shifting properly at slow Rev, check the oil,

 

check the tranny fluid and it might be a good idea to take it to a tranny specialist to check the sinkros