Hi Vince, Welcome to the YOC, unless he put car oil in then most motorcycle oil will be ok, car oil has loads of addatives in it that will make your clutch slip but not stick them together, it might be that you have the wrong springs in or the old ones are weak, did he change the springs as well? other than that the best you can do is take the clutch plates out and see if they are still straight as a bent plate can make the clutch behave in the way your describing. Try measuring the springs when you get them out to see if they have the correct length, (look in your manual for the sizes) as they can become compressed over time. that's the best I can come up with without looking at it myself hope that helps a bit.
PS you will get more feedback to your question if you do an INTRO in the new members section as folks like to know who they are talking to.