Stopping a minor coolant leak from the thermostat housing?

The car is a european 2003 ford fusion with 1.4 petrol engine. Absolutely identical to the mk6 Ford Fiesta (same car, different body).

So, today I had the car serviced at the dealer, and they discovered a coolant leak from the thermostat housing. After driving home, I left the car parked for a few hours and returned to find a small puddle of coolant underneath it and some fresh drops of coolant dangling from the engine block. I followed the path of the drops and found the source of the drops - i.e. the underside of the thermostat housing - but I haven't had time to get a mirror to see what the leak looks like (it's in a hard-to-see place behind the alternator and under the intake manifold).

With labour costs, and gasket, the dealer is asking for €250 to change this housing (worth €25) and the alternator belt (€88). Frankly I'd rather not spend the money if I can avoid it.

I'm thinking - since it's only a small leak, is there any way I can try sealing it off from the outside? Like maybe putting a layer of silicone, superglue or epoxy (araldite) on the housing over the leak? This part only heats up to around 90 deg. C (engine operating temp) so heat shouldn't be a problem. What I'm concerned about is possible reaction with the chemicals in the coolant, and getting the glue to stick and hold on for a couple more years.

So - any ideas how I should go about it? Best method to use, best choice of adhesive or sealant etc.? Maybe you can think of a better way? (Except for putting stop-leak in the coolant).