A warning for all - there is a seller of these on Ebay who trades as wfxpress and advertises as follows:-
NEW AW 55-50SN 55-51SN AF33 New Linear Solenoid Kit SAAB Equinox Maxima Volvo. The advert is well written in very good English, the seller gives his location as California.
WARNING I bought a set of these, and when they arrived they were clearly second hand. I immediately lodged a claim through Ebay (who needs to risk all that bloody work to install second hand units of indeterminate quality): the sellers' response was that he had used the word 'other' along with the word 'new' to indicate that they were in fact not new. In short, he is a con-man, and a liar. I now have to wait another week for genuine new parts to arrive.