What has failed to be mentioned here is that your A/C system already has dye in it. You had stated that it has been converted to 134A and that you noticed greed fluid on the side of your transmission. A lot of compressor oils come with the dye already added to them.
Use a UV light and shine it on the suspect area. If it glows then you have a leak in the suspect area. You can also confirm this with an electronic leak detector. Carefully insert the sensor tip into the evaporator drain tube. If the A/C has leaked enough to stain your transmission then the detector should have no problem picking up the 134A.
I would recommend you stay away from any kind of sealant for your A/C. It's not worth risking ruining your A/C compressor IMO.