I’ve had issues with the cup and the bias spring, generally speaking if you have issues with 3rd and 4th it’ll be the spring -,which are like rocky horse dermot to find, you might be lucky and find one one on eBay.
I got some spring steel wire from a local Spring Manufacturer and made a couple . If you go down this path make sure you do all bending “cold”, then put in the hottest oven you can muster for 1/2 an hour to stress relieve - only cost a couple of quid for the suppliers. Coffee Fund
Cheers
