1999 355 Spyder F1 Clutch/Wear/ Adjust

Just had a service oil change etc. They said clutch has 70% and its slipping a bit in first. In some instances I do notice that. They said I can probably eke out the summer then need a new clutch.

Question's are;

1) Is 70% the magic number for a clutch redo? I would have thought 50% but that's just a guess remembering growing up driving standards.

2) If the slippage in 1st persists, isn't there an adjustment that can be done?

Just curious before I drop the $4K they are estimating for a F1 clutch overhaul.

Thanks

~Eric