I would ask them to do the dye check on the A/C. I have a 95 E420 that showed leaks in the evaporator, expansion valve and a hose. I went ahead and had the hose and expansion valve fixed, system recharged and all has been well for several months, so hopefully the dreaded evaporator fix can be delayed for sometime. As far as the groan when applying brakes my brake pedal occasionally makes a similar noise but nothing to do with the brakes. With 55,000 miles you will be coming up on the 60K service with dist cap, rotors, all fluids, etc but most of these can be DIY. My radio works great and I would say the antenna extends about 30 inches. Need to make sure the antenna is kept clean for smooth operation. Will dealer supply CARFAX report?

The E420 is great car and if you are reasonably mech inclined, you can do many services yourself. Another key is to find good independent shop. I'm fortunate in Cincinnati to have Precision Motorcars Good Luck