Hey guys, been driving my bugeye around for about a month now and just today shifting from 3rd to 4th has become noticeably harder and makes a bit of a 'clunk' going in, not grinding or anything though.

Admittedly I was a little rough on the clutch and gearbox at first, but I adjusted pretty quickly and I've been driving it smoothly for weeks and this has just popped up today. If I hold the clutch in longer than usual then I can sort of nurse the stick into gear by slowly moving it down and I won't get that clunk, but that's not much of a solution.

Should I drain the gearbox and give it new oil, or does it sound like I've broken something?

Thanks for help.