Just in case you havent found your problem yet,

Mine turned out to be a bad drivers side acceleration sensor. Took a while to nail down because it tested to spec according to my WIS initially but after exposing it to prolonged heat it failed the test.

The thing that got me on the right track was I have an electronic throttle control module cover on the drivers side of my car (129). It also covers the acceleration sensor, the wiring that goes to the fusebox, along with the ESP brake pressure sensor. I found that when I removed this cover to test the wiring and sensor and left it off, this dissipated enough heat so that the ADS wouldn't trigger a fault. as soon as I put the cover back on and drove it for a while (at least 30 min or so as you describe). ADS light would come on. I figured it had to be heat related resistance issue....

One thing that is different about our symptoms is that my console light would stay off even though the ADS light in the insturment cluster would come on.

Ultimately your issue sounds also like an electrical heat resistance issue. Perhaps you may also want to look at the damper valves (subject to exhaust heat) or see if the ADS stores a hard code (mine didn't). unfortunatley the only way to read those codes is with a HHT or SDS (dealer or really equipped independent shop)

Hope this helps you or someone else who may be experiencing a similar issue in the future.

Good luck let and us know what it turns out to be.....

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CR

97 SL600