After cleaning around the bellhousing to find the source of a small oil leak (turned out to be dripping from the rocker cover seal) I put my finger in the bell housing drain plug to see if there was excess oil only to find a washer. Managed to fish it out and its the pivot pin cap (FRC2975)

Is it going to be a problem to run without it? What is the actual purpose of it?

I just looked up the part number and did not recognise the part and can definitely confirm I do not have one fitted. I have had my gearbox out several times (long story) and replaced clutch/arm etc, this year. What engine and gearbox do you have? I am running a 200tdi and lt77, so if you have a similar setup then it will definitely be fine without one. Looking at the parts diagram I am guessing it is supposed to sit between the pivot ball and the spring clip on the back of the release arm. The lack of one fitted would explain the grooves worn in my pivot ball and the reason I replaced while it was all aprt, but it caused no problem in operation before replacing, and has not caused any problem since without the pivot pin cap fitted.

Its a TD5 and R380 box. Thats what i thought maybe the the spring clip goes behind the cap it and hold the pivot pin into the bush?