Thanks again for all your suggestions!

I took the seals off and soaked them / shaked them in acetone and let it sit for an hour. Then I took a can of compressed air and blew the acetone out and repacked with Triflow waterproof grease with a syringe. The headset is now as good as new!

As a precautionary measure I took some of the waterproof grease and made sure to grease the rubber lip of the headset cap and put an extra layer of grease on top of the cartridge seals.

Thanks for all your help!