Recently my chain snapped and the derailleur fell apart (it's sort of bent out of shape & it is now in two pieces). It is a Shimano SIS derailleur. I have bought a new chain and a new Shimano SIS derailleur. The new derailleur is not identical to the old one, so my main question is: Can I use the new one to replace the old one AND have it functioning ? Thanks for your help!