Plastic head stay part
Is it white?
Is it inteneded to furl a sail OR merely to hoist and lower a headsail?
If you look at the "feeder" where the sail luff tape enters the plastic part, this ought to be Stainless steel and may be stamped with the phrase Tuff Luff and a number sequence like 1506 for instance.
AND if you study the feeder carefully you may see a second "Groove".
IF there is no such SS feeder
OR if the plastic is Grey
OR if there is a furling drum
THEN you will not have a tuff luff but perhaps a CDI furler.
In the case of Tuff Luff, you have a Tuff Tuff manufactured by Schaefer Marine in Newbedford MA and available thru most riggers.
IF a CDI google them for support.