I'd suggest looking at this plugin - Field Repair This next bit is rather self serving, however, I'd answer Tony, also, as I am curious what he's going to say
I'm also curious about this, if in a quest profile, there is a way to hard code in a /summon mammoth, then force repair and vendoring of greys.
Ahoy ahoy. So I was looking to do this as well for a profile I'm writing. I found the HB wiki pages to be very helpful, particularly the pages on custom behaviors. I successfully used a RunMacro behavior followed by a ForceSetVendor behavior, with only appropriate parameters included. First things first, at the top of your questing profile under the <Vendors> tag, include the following line: <Vendor Name="Gnimo" Entry="32639" Type="Repair" /> Second, and lastly, include these two custom behavior lines whenever it is in the profile that you would like to force your bot to summon his mammoth and repair/vendor: <CustomBehavior File="RunMacro" Macro="/cast Traveler's Tundra Mammoth" /> <CustomBehavior File="ForceSetVendor" DoRepair="true" DoSell="true" /> This may not be exactly what you were looking for, but I hope it helps somewhat.
In QUESTING and ARCHAEOLOGY mode if you type in "Traveler's Tundra Mammoth" for your ground mount it WILL sell and repair anytime your paramters are hit be it durabiliy<x or freebagslots<x. You can also download an addon from curse called "CrapAway" and it will force sell all your greys. I also use a addon that will auto repair anytime a repair vendor is open also found on curse.
mine mounts runs off just a little and then opens vendor are you sure its running all the way to vendor and i dont know if it makes a difference but i use singular if you arent using it try it and see if that fixes it