Got into the leaking coolant situation today, I can tell you for certain what it was not:
Not:
1. Water pump (at mounting or at shaft)
2. 90 degree adapter
3. O-ring for adapter at t-stat cover.
What I found however was not impressive, there was evidence of leaks with pink coolant on the bolts for the PS pump mounting bracket and at the bolt heads for the t-stat cover but otherwise everything was dry as a bone.
View of t-stat cover from the side. Yesterday this was more clearly wet. Today it looks moist but not as much as before. The mounting bolts did have pink coolant on them though.
Shot of the flange from below that also does not look leaky.
So because everything was out of the way and because I had parts on the shelf I pulled the existing flange and replaced it with a new one complete with new o-rings.
The existing flange looked fine, it wasn't cracked anywhere or warped too much and the o-ring for the 90 degree adapter was fine too. I will say though that the thermostat o-ring seemed to be less than stellar and I'm thinking that it just wasn't up to the task.
When I removed the old flange the thermostat was stuck to the o-ring which was stuck to the flange, which seemed odd to me. And they came out without any fighting at all, as though the o-ring was really insufficient in size to keep from leaking when under pressure.
So, it's all done and buttoned up and the cooling system has been refilled and driven up to temperature. Tomorrow I will top it off as necessary and then take it out and warm it up again. When I got home tonight from cycling club I noticed just a slight odor of coolant, nothing like before, which I attribute to residual coolant in the nooks and crannies of the engine from having drained it today to do the replacement.
I was happy to see the WP was not leaking anywhere, that would have been the second WP to go on this car in short order, the first being a Gates. I will say though that for some reason the PS (and WP) pump belt tensioner was loose and it should not have been.
Steve