You got me Matt... I do not know. He changed many things as they appear new. Particularly hoses and fittings. The Accumulator appears older though . The switch does not really appear that old but I cannot be sure. He had it done. But he had no real records of exactly what was changed and what wasn't changed. When I got the car it was working but just weak. So we charged it (suspecting a leak but never saw one) and it worked without fail from then on but I haven't really used it too much either. But this is the first evidence of any leakage. Fairly suddenly and probably when parked it today I would say.

Added on edit: looking at the online catalog here I see that the Low pressure only switch is more of a metalic Brass colored body and this one on my car appears more Black Plastic so I am going to guess it is a High/low set up like it has been replaced at some time.

I found this parts description on a High/Low switch online just now...

1977-1993 Mercedes Benz 300D - ACM A/C Pressure Switch Part Number: W0133-162826
Description:
2 bar low pressure and 30 bar high pressure binary switch. This switch is designed to be compatible with R-12 and R134a refrigerants. Located on reciever-drier with 2 spade terminals. Used for compressor cut-out..