Help finding wiper seals Billstein struts

[Procul]

'78 SC
What are people using to replace worn rubber seals in Billstein struts? I haven't been able to source the part.

I purchased Billstein B6 inserts, but need to replace the rubber seals that sit below the metal caps, they're hard as rock. Talked with our hosts, their suggestion is to buy a pair of complete front struts at $1,154.00 each to get this $5 gasket.
The metal cap is fine but I need new rubber. This seal has a spring collar.

[reclino]

For 40mm struts this shows as a spare you can order from Bilstein for $12. Summit racing lists it for $18.
Genuine Bilstein 40mm insert seal.
E4-B36-800A

[Procul]

Wow that was easy, thank you. I'm gonna have to learn to search better