I have the same problem on my '88.  Corrosion and leakage around the waterpump, thermostat housing and from some hoses.  I thought that using the phosphate free orange stuff would be better that the green.  I've found some interesting articles on this orange stuff.  One article stresses the importance of the 50/50 mix.

Jim Bowen
'88 Wolfy Weekender

http://autorepair.about.com/library/weekly/aa052601c.htm

http://imcool.com/articles/anitfreeze-coolant/dexcool-macs2001.htm