I found this listing for a yoke that I believe fits the A518. The spline cut is way different. Is it possible that both the yokes you have are meant for the 727, but just different tolerances depending on manufacturer? Wouldn't be the first time an aftermarket piece doesn't fit correctly.
http://www.ebay.com/itm/350483255359?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648#ht_500wt_922