This end cap is no longer available but we do have the seal that is installed inside the end cap.
Usually only the seal requires replacement.  Seal available here.

Stanchion End Cap 068161
For 30 mm Black, R7, M30 etc
Black plastic  29.7 mm OD, 20 mm tall
1.125" 18 TPI upper thread
22 mm lower external hex

Manitou Part Code: 068161