Thanks guys.
Yes definitely bearings, I can see them down in there. Just like this except blue pulleys https://www.svb24.com/en/easylock-easymatic-two-speed-mainsheet-system.html
I'm trying CRC Onedrop C&C synthetic, as a cheap alternative to Mclube Onedrop.
https://www.crc.co.nz/One-Drop-Range/6895-b9b7dd31-2386-4855-b55a-00ffc53b3f5b/#Popup-Closer
6 bucks from Steves Marine Supplies.
Cleaning them and dropping from 12mm to 10mm when I buy a new mainsheet from Knot Me will make the most difference I'd say... until I can slip new blocks past the bean counter.