Peugeot 308 Coolant Leak

[JimM169]

Noticed the coolant was low on my car at the weekend and having a poke around underneath I could see a few drops running down the gearbox casing. Checked the hoses etc but all looked OK so guessing it may be the thermostat housing? I couldn't feel anything around it but it's difficult to fully access so may have missed it?
I've checked online and new housings are £200ish !! So rather than shell out for a complete housing what's the likelihood that it's just the seal that needs replacing or is there a history of these units failing?
Has anyone done a seal replacement and got any advice?
Is there anywhere else I should be checking for the leak on that side of the block before I pull it apart!

Car is a 2015 308SW 1.6 BlueHdi 120bhp, VIN number has the BHZ engine code which I believe is the DV6FC variant

Thanks in advance for any input you can give