If you do go with the 134, it will not cool as well as with the 12. This is a fact of life. The systems that are designed for 134 do cool just as good as the 12, but when you convert, you loose capacity. I would find the leak and use 12.
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM