Clutch slow to release especially in 1st

[b1k3rdude]

 that spray, isn't the easiest to find for sale.  

As Gnasher will probably tell you - WD40 is fine for penetrating, but not really lubricating.

That DoubleT I found in my local auto factors, and again channelling my inner Gnasher, I imagine he would say GT85 should do the trick...

So yes at a push you could clean out the cable with WD40, but then liberally flush with GT85, or just clean and flush with GT85.