For those who don't know, if you look inside your right front wheel well, you will see the clutch hydraulic line dropping down to the join between chassis and body. If this is black plastic, you should really get it changed, or it can swell on hot days and prevent the clutch disengaging properly. I know of at least one circumstance where this line has actually burst.
The proven solution is to replace this plastic line with a stainless braided teflon lined hose. I offer this part for £49 incl P&P and can have it made 800mm longer for right hand drives (I keep it running on the left side to avoid the heat from the heater matrix lines).