Those styupid cooling plastic bits don't degrade only due to heat cycle. they also degrade if the coolant isn't changed every 2 or 3 years. Apparently the additives break down, and then it will start degrading the plastics as well (and the aluminum).
on the e39 forum, it's been documented that the guys who actually change the coolant every 2-3 years don't experience that exacerbated plastic embrittlement. I always changed that blue coolant every 2 years, and never had a problem with the cooling parts. I changed the cooling plastic/rubber parts as preventative maintenance after 8 years, and the parts looked really solid. What broke due to embrittlement were the 2 air channels from the microfilters to the firewall. That was after 10 years. Both of them.

interesting about the coolant changes. my car was serviced at the dealer for the first 7 years. maybe that is why the stuff has held up to this point. i am sure the coolant was changed with some regularity.

FYI--the connection is a push in to release connection.