replace zoom unit for SD1300 IS

I'd like to repair the broken zoom unit on a IXUS105 \ SD1300 IS \ IXY200F.
Could anybody tell me how to figure out what part I need?
the issue is, I saw on ebay a zoom unit for the IXUS120 \ SD940 IS for 50$, while the unit that's for my model is going for 100$, yet they seem to be exactly the same.
how do I find out if they are indeed the same unit?
Thanks a million

p.s. the ebay items are

IXUS105 \ SD1300 IS \ IXY200F- http://cgi.ebay.com …K:MEWAX:IT#ht_1​489wt_1000

IXUS120 \ SD940 IS- http://cgi.ebay.com …RK:MEWAX:IT#ht_​4493wt_961