Wouldn't that be the metal collar (?) on the older PRT's that you could cinch down a bit if they were weeping? Newer PRT's had a brazed collar that if you tapped them would break and leak even more. Is this for the 71?
"Why do thy think that their rubber is so much more valuable than everybody elses? Is it excised from the whelted buttock of some high ranking supplicant at madam Swartz's House Of Pain? Is it pre-soaked with the quim of alien virgins? Do they hand deliver it and fit it for me whilst plying me with Bolinger and tickling my baw sack with a Dodo feather?"- Bonkers the Dog