What is this? Maybe a manual transmission leak?

the MT transmission level checked out ok today at its 170k checkUp, there's about 20k on that fluid and level still good so may or may not be that
when the weather and ground warms abit i shall drop and roll back under to clean the sheepgrease and re-wax that area, see if it comes back

its possible that old engine oil from the filter change (that got on the splash shield/skid plates) blew back that far, i do recall it was windy as all heck out that day afterwards on US-20 heading west for several hundred miles, i could barely keep the truck on the road hahah with the head-on winds and MPGs blew bad

 

Doesn't look like anything to me. Check back to see if it starts getting bigger. Good thing you have pictures to compare as well