Looking for expansion tank cap

[turboturner]

g'day:
First run of the season (7 months off), my expansion tank cap was leaking, vomitting into the overflow bottle, (which had no vent, I discovered), & spewing coolant overboard (KF IV 912ULS which has been flying like this for a decade). I drilled a vent, no more spewing, but, zero water pressure. I suspected the cap, flipped both rubber gaskets & cleaned the contacts on the expansion tank. Pressure now back to normal, but I think the cap spring may be tired and am looking for a backup (I fly in the boonies and would hate to be grounded for a bad cap). Rotec wants $112 for a new one. Any thoughts on a cheap replacement cap? Mine is a 0.9 bar (13 PSI) but Rotec tells me the new ones are set to 1.2 (17 PSI). Thnx for any tips.
Carl

[93EG]

I don't remember the number but it's same as a BMW motorcycle.

Ed

[turboturner]

thnx Ed. I'll look into it.

[Guy Buchanan]

Should be BMW 17112345074. Many sources via Google.

[turboturner]

thnx Guy! Much appreciated.