I don't know what product the tech used, he just said "fluorescent dye" was added to my system when he topped it off with r-12. Next day I brought it back, and he found the very small leak - said I could use the system until probably end of summer and he would keep an eye on the r12 level whenever I brought it in for service. The fluid in the sight glass was yellow brown after he added the dye. No problems running it during the last couple of weeks.
87 300E, 65k miles