D60 coolant leak followup 2000 lxi

[luckyron1]

Had it serviced, and the leak checked out in Dallas at the Allison
Transmission/Detroit for what I thought was going to be just a loose
hose clamp. Turned out that the coolant was dripping out from a
rusted thermostat housing which of course is only accessable thru the
AC compressor etc. It was dripping down on the wet hose that I
could see from underneath. They showed me the leak with a flashlite
and it's for real. No one ever said that these bird engines were
easy to work on. So... they tell me 5 to 7 hrs of labor plus the
parts, probably obtainable from Detroit Diesel. They did a pressure
test and it scored 11 out of a possible 15 psi. It's ok to drive it
but I'm to keep a close eye on the coolant level and temperature
gauge. They say it's not urgent but that the work should be done in
the next few months or so. I'd like to wait until we return to the
midwest, from San Antonio, in late April. Anyone had a similar
experience and do you think I should rush it or wait until late
April? It leaks a gallon after driving 250 miles or so.

P.S. Can I get by with topping off with pure distilled water until
then or should I put in the 50/50 mixture recommended by Detroit?
And before I forget, thanks to whoever it was that referred me to
the Dallas shop noted above. A very clean, friendly and well
organized facility which I would refer to anyone.

Thanks guys!

Ron & Ruth near Galveston