To be honest here, if Brewer's didn't find anything wrong when they had you car in the shop we aren't likely to find it via internet, but you never know.

There are a few spots where the linkage can bind up thats why I you want to try this first and we can go from there. I have seen bad springs before but only 1 or 2.

I have had the adjusting nut back off on cars before. Adjust the play and mark with a sharpie and see if it is moving.

Then if it is, come up with a way to secure it. Double nut, new nylon nut, etc.

You could even have a problem with the nut pulling through the rubber insert in the fork eye. Make sure you have a nice thick washer of some sort between the rubber bushing and the adjusting nut. I left one out on my car this past year as it sat for several years and parts got moved. It worked good for awhile and then pulled through the rubber.

I'm pretty sure your car is losing the adjustment if it works good for awhile then starts having the pedal not return.

I bet when it happens it returns a little bit but not all the way, correct? Have to pull it on up the last couple of inches with your foot?

I'll bet the problem is in the clutch fork pivot area where it attaches to the throwout bearing. New parts took care of my problem. I can't remember exactly if it was the fork or the throwout bearing but my mechanic took care of it.

I had the problem with the clutch pedal not returning fully in my old Duster340-4spd car and that was the problem. I also had the Hayes street/strip clutch unit in my car.

Also a torque strap took care of my issues with noises/clunks from the motor raising up on takeoffs. Check your motor & transmission mounts too.