Coolant leaking from thermostat housing

Hi all,
changed my serpentine belt yesterday and noticed reddish fluid on the inside of my skid plate. I changed my oil last weekend and didn't notice it then, so not sure if I just missed it or if this is a new leak. I just got the truck two weeks ago. Anyway, I was able to trace the leak to the thermostat housing where I see a little bit of coolant pooling at the bottom of the housing (see third image below). Before I go and get a new gasket, is there anywhere else I should check for leaks? This does seem like it's the spot, but is there an easy way to check the water pump? Water pump and timing belt were done 25k miles ago.
The coolant in the reservoir is slightly below the L line. Checked the radiator cap and level seems fine there, for now. I will probably get a gallon of coolant from my local Toyota dealer tomorrow together with the gasket and top it off periodically until I get to it.
Any other suggestions? Thanks all!

 

Top it off. Hose off those area. Drive it till up to temp and carefully inspect common leak areas for drips. Refer to Shifty’s megathread

 

Thanks! I did check @shifty` s thread and found other common spots to check! Do I top off the reservoir or at the radiator cap?

 

If reservoir is not empty then radiator is probably full. If top hose is stiff when warm it it. Only open radiator when cool or risk serious burn.

 

Definitely good advice, thank you! Will get some coolant and top of reservoir. Thank you!

 

Update: Replaced the O-ring today. The old O-ring didn't look that bad, maybe a little dry, but not brittle or anything, so no obvious reason it was leaking other than old age. The job took a little longer than expected, around 4.5 hours, mostly because I took my time cleaning the old FIPG material (still the factory gasket I believe) and I was trying to figure out if I could get away with not draining the block (spoiler: I could not, spilled coolant over the pulleys and belt, cleaned that up with fresh water). Overall not a bad job at all, refilled with Zerex coolant and made sure to get all the air out. The coolant that I drained from the radiator was more red than Zerex pink, hope it's okay to mix? Attaching some photos below. Went for a test drive and hope for no leaks tomorrow morning, it was only leaking when the engine was cold with a half full reservoir.