At 09:56 PM 11/18/2011, Frank Lee wrote...

>Or patch the hairline crack in the old tank..

I can only say that on a previous van we had (Toyota), I was able to
successfully extend the life of a plastic coolant overflow tank using
JB Weld. AIR, I cleaned it well with soap and a degreaser, scratched up
the area around the crack with some sandpaper, cleaned again with
alcohol, and slopped on the JB Weld. It lasted at least 50K miles
afterwards. YMMV.