What is the likely source of my W210 refrigerant leak?
 

My son's 98 E300 has a bad AC leak. Today I had the chance to add some refrigerant to see what was going on. After getting up to about 1.4 bar of pressure, I turned the car off and heard a very obvious hissing sound from the left front. With a leak detector I was able to determine that the source of the leak is directly beneath the front washer tank...it's a very precise spot that sets off the detector.

Could anyone hazard a guess as to what's leaking and what's involved in effecting repair before we go any further?

Dryer is in that area along with some hoses. Pull washer reservoir out of way and you shold be able to find it.

Confirmed, the dryer is directly beneath the left headlight. You have 2 sensors and 2 hoses at the dryer so lots of potential for leaks.

Note that MB updated the stub hose from the condenser to the dryer so be sure to order one if you end up replacing the dryer.

You may end up getting lucky and it’s just a loose connection.

You can soapy water refrigerant leaks like any other air leak.

As a data point, the dryer on my w210 literally blew out due to rust.

Great point, the bottom of the dryer is exposed to the road. It sits in a circular opening in the body and would be exposed to road salt.