When I walked out to my car and found the puddle of coolant under it the first place I could find that was wet was the thermostat elbow ... so I thought the gasket had let go. After I got the car home I took off the cam belt cover off and saw that the water pump was leaking and the cam belt/pulleys had thrown the coolant back up onto the thermostat elbow even though it (probably wasn't) leaking but I had already decided to take it apart and change/reseal it anyway so here we go ...
heres the old one taken off ...

Pretty cruddy.
When I had ordered the pump from the UK I had also orded the theromostat (and new seal and retaining ring) ... just as well 'cause I had a right pain of a time getting the old one out. After 25 years it was proper stuck [:(!]
On the outide I was surprised how good it looked but when I tried to take out the retaining ring ... oh my god ... the seal under the thermostat had swollen and hardened and I couldn't get the ring out. I took it to work and got the assistance of an extra pair of hands, a heat gun and a couple of screwdrivers plus a pair of pliers ... and finally got out the retaining ring.
Long story short ... I cleaned up the thermostat housing inside and out, and got it ready for new seals and a splash of paint ...

Then I got all the new bits together (seal, ring thermostat and bolts) ...

... and assembled it

Here she is, bolted up with some paint-on 'Hylomar' instant gasket. How long do you think those belts will stay lined up [x2x] Note the new coolant hose, clamps and bleed plug (no clamp on this yet ... I'll do this after I've bleed the coolant system when I first run it

Oh my those pulleys [V] ... a job for another day ...