New to the forum, bought an S4 today, very happy with the car, goes well and sounds well

Just a quick query......
On driving home from Glasgow to Norfolk, I hit the A1 and there was a lot of start/stop traffic. After a while, there was significant clutch judder and I couldn't engage first gear (was ok up to the A1) had to be pushed onto slip road, where I was able to engage 3/4/5 gear, and slip the clutch in 3rd to get moving.
Was ok once moving, floored the accelerator in 6th at low RPMs but clutch wasn't slipping. Now my question or theory lies with possible clutch fluid leak or clutch master cylinder (or equivalent) and was just getting the feelers out really to see what peoples opinions might be.
I spoke to the seller, who is a great chap and has offered to help out with any repairs, i'm hoping it's a master cylinder really

Perhaps someone can advise where the location is of said cylinder, to add there was no leakage on the floor of any description, and to add, there was a recent gearbox fluid flush.
Thanks for any help

P.s. awesome site
