I know this is an old thread, but what was the "correct cap" for the Motive Bleeder? My ST is a 2017, but it looks like Ford has the same part number for all years of STs.
Motive recently told me they don't make a cap for the ST, but I could risk it on their 1108 (for some GM cars). They misquoted me the diameter of their cap as 1.8" (like the OEM cap) but theirs is actually 1.9". To get it to work at all, I had to use the very thick washer they provided, which required an excessive amount of pressure to engage the three tabs, and the cap does not "click" into place like the OEM, when the tabs are full engaged. I don't know if its related to the bad fit, but even at 10 lbs. of pressure, it started leaking from where the tube joins the cap.
Any help would be appreciated.