I'd just put up the yagi, and likely be done
with it. That should get you over the hump well
enough to use the repeater.
You probably don't even need a rotor.
Just aim it at the bad machine, and if the
other one is as good as you say, it will likely
be usable even aimed at the other one.
Or you could use a switch to go back to the
vertical. If the coax run is long, don't use
thin coax like RG-58 or it's ilk. I consider
RG-8/213 types the minimum for anything semi
critical. And you can get better than that.
Doesn't pay to use a gain antenna if you lose
a large chunk of it in feed line losses.