Installed a brand new Sram Force compact crank (pretty big bucks) on new bike am building; spider is warped so that the rings are warped as well and lots of chain rub on front derailleur which I can't adjust around. The bike shop folks that sold it to me on Ebay are stand up and will send back to Sram as a warranty item--apparently you have to go through a Sram retailer for warranty problems. Is this an isolated matter or a regular problem with Force? Should I just bail out and go back to Shimano or FSA for a compact crank? My shifters and derailleurs are DA. Thanks.