96 Jetta GLS, 2.0L - burning coolant?

for a couple weeks now, i have had a nagging problem with the cooliing system in my 96 Jetta GLS.

i am steadily losing coolant in the system, but i am unable to find any kind of external coolant leak, except for a small leak from the seam around the middle of the expansion tank. but even that only seems to show up if i crack open the expansion tank cap to relieve pressure. the oil looks normal as well.

i was told that the car might actually be drawing in coolant when cold, but burning it off at running temp.

any advice to get going in the right direction with this is HUGELY appreciated.

not really sure how to check it, but my sisters 96 2.0 was losing coolant to the trans via the trans cooler. coolant would enter the trans and eventually be burned off.