Clutch dragging - replacement advice please

[stay_upright]

I believe one or more of my clutch plates has warped and the clutch drags even with the lever down to the bar.

This meant I failed to get off the line first kick at a race this sunday and also I was stalling 15-20 times in the race - not good. The bike idles fine in neutral but stalling in gear with the clutch pulled.

So my questions - has this happened to you - what was your fix?

Is it common to warp plates?

Should a new clutch mean there is no drag at all in gear with the clutch pulled?

A while ago it was dragging a little and I thought I could tell one plate was a bit warped by laying it on a bench - is this a good or reliable method? The others looked flat.

I was using 10w40 petrol engine oil - could this have contributed to them warping? The advice I get off everyone who runs this says it's fine...

I will probably end up with a DP replacement clutch - are these good?