It does sound like the valve and/or solenoid is bad. You measured 27 volts, but that's only about 10% above the specified value, which is pretty close for a random transformer. The voltage will likely sag as you approach the rated current draw from the transformer, but even if it doesn't that's pretty close.
Freeze the pipe
I've heard tales of stopping a pipe for valve replacement by freezing the water but I haven't ever attempted it. Take this as an entirely untested theory. I suppose it might go something like the following.
Choose a location on the pipe sufficiently far from the valve to be replaced and pack dry ice around the pipe. It's probably a good ...