Crawling under the car last night, the vacuum line from the manifold to the modulator is metal except for the last four inches. Except where I cannot reach or see it as the line passes behind the engine, it appears intact and in speaking with an MB tech on the phone last night, the 4 inches of rubber hose indicates to him that some work was previously done since he says the entire line was originally metal. The grease and crud over the modulator tells me it hasn't been fiddled with in many years if ever, but rubber hose appears tight and still flexible. Since I'd also pulled the lines from the bottom of the radiator installed two days before to make sure there was no blockage, and blew ATF all over the garage floor and myself when I turned on the engine, and had cleaned up, refilled the tranny and the car was off the ramp, I'm to call him back tonight.
Absent a vacuum tester, we are going to presume vacuum and he will walk me thru a test of the modulator after I get the car back up on the stands tonight.
I'll take your advice and seek the posts you mention too.