There's nothing inside the TB cover to leak coolanat. Lots of other possibilities. You can visually inspect the plumbing in the front lower part of the engine. If it looks like it's coming from the top front of the engine, the best way to inspect it is to remove a cooling fan (I usually do the left one). The last time I saw something similar it was a loose gear clamp on coolant hose to the thermostat, I've also seen this large Y shaped hose crack. Another time it was the thermostat oring. I've also seen the crossover line at the top of the rads leak. A really common one to watch for is the grommet on top of the reservoir tank rotting out...In that case it will only leak when coolant is exchanged from rad to reservoir.