I know two W140 owners that have tried the CryoSeal. One is working perfectly, with no leak whatsoever. The other is still leaking, but a slower rate.
Is there anything to lose? If it doesn't work, I can't see it mucking-up the repair in any way.
If Steve can do an evaporator in a W140 for $2500, that's a good price. And I doubt there are too many people around more knowledgable about MB AC systems.
1998 C230 "Black Betty"