Replacement for 9-speed Shimano Tiagra GS

rgluke Posts: 10
edited March 2014 in Workshop
Hi, I have a 2009 Shimano Tiagra GS 9-speed rear derailleur and have lost one of the jockey wheels after one of the bolts came loose; is it worth replacing the jockey wheels (if so, which type/model?) or should I replace the rear derailleur - if so is any 9-speed GS/medium cage suitable?
Many thanks