I have seen the Cats come loose and knock a bit. I always start on the easy side then work toward the hard stuff.

On the A/C, I have not been able to get a good 134 conversion on a 300E as of yet. The system was not set up for the larger molecules of 134 and the oil gets absorbed by the hoses over time.

I would find the leak, then use 12.

PS, you can check for evap leaks by taking out the blower motor and looking in.

__________________
Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS