Ed:
I am surprised more people have not complained about this. It sure looks
like a poor design. I take both parts out and clean the affected areas
thoroughly. Getting the pipe out is a real feat of flexibility, the
thermostat housing is not much better. I clean the lip end of the pipe
with a wire wheel mounted on a bench grinder. I used the ultra fine wire
because the metal on that end is so thin from rust. Clean out the inside
mating surface of the thermostat housing as well as you can. I used a
small wire wheel drill attachment.
        Now re-assemble the housing to the engine. Work the pipe  almost
into position. I then apply a thin layer of Permatex Ultra-Blue in the
groove and seat the O-ring. It is best to do this AFTER the end is past
the pulley. Apply a thin layer of Permatex to the inside of the housing
and around the outside of the O-ring. After everything is assembled I try
my best to pack some more Permatex in behind the O-ring for extra
protection.
Drive Safely & Good Luck
Ken Lewis     <Kernersville NC, The Heart of the Triad>
86 VW Transporter Three Door Pickup
60 Porsche T-5 Coupe
85 VW GL Vanagon<Elvis>lives again!