Brother of The Benz, Bob
Consider the age of your beloved and the labor required to gain access to any one of the vacuum elements.
Remove the A/C, heater housing assembly completely.
Renew every serviceable component, i.e.
vacuum elements
evaporator core and expansion valve(the evap comes with a new x-valve and seals)
blower motor assembly complete
replace all of the seals and gaskets in the housing
completely disassemble the housing and thoroughly clean it
inspect the heater core and replace if required
Your assembly has lasted 17 years, why not give it a new lease on life?
I recently had my unit rebuilt on my 1987 300E after 14 years and 177,000 miles as I'm recommending to you.
In addition I had the compressor/clutch and the drier/reciever replaced. The condensor is alright and to rreplace it does not effect the low pressure side of the A/C.
Mine is a one owner, that's me, Benz; and I intend to drive her until I can't drive any more.
It ain't cheap, but do it right and do it once. Don't have a component fail next month that was overlooked today.
Happy Trails Beep Beep from The Spiderman in Houston!!!