Help!! No reverse

[Marc-1]

1991 300 SL (automatic transmission)
No reverse ... brought the car in for a rumbling sound and then the check engine light came on. It was a simple thing, at 15 years old the rubber on these (and most anything) cracks and breaks. The flex disc which is where a universal joint would be, had broken, spun around and unpluged the oxygen sensor. A $130 part and I thought I was on my way. Now I have no reverse. I brought it back to that dealer and they said all the linkage is correctly installed and they assume it's internal. They suggested a remanufactured trans.... And the answer is... NO!!
There has to be something simple wrong because it's my understanding that the 1st gear band is the same as the reverse and 1st works! All 5 forward speeds work perfect. If a spring broke in the valve body which would engage reverse then I need disassembly help. To the best of my knowlege there still are no manuals available on this car so where do I go???
Please help me with this one...

[whunter]

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[stevecora46]

Reverse bands in my 92 300SL gradually wore to the point that reverse woudn't go anymore. Just like putting it in neutral. Transmission shop charged $1700 to replace worn bands. They said this transmission is known for this and will probably do it again in 100K miles. Mine had 89K on it. They also mentioned that the wearing bands drop debris into the tranny, plugging filters and valves, which also leads to poor performance. Transmission works good now. By the way, two other shops quoted $2700 and $3000 for the work. Shop around, it pays.