So, since I started this thread, thanks for all your responses! Besides killing it with the brake/HST combo, have learned also to manually kill it by moving the speed control plate in the engine compartment.
Today, finally took the stop solenoid to the dealer - asked the parts desk to test it - of course, he came back and said it was shot. (can't help but feel like the classic fox/chickenhouse...) anyway - still need to learn to do that type of test. Found an older thread from 2007 with diagrams for that.
Installed the new solenoid. still didn't shut off. Checked the fusebox a second time - the 10A fuse for the timer relay was broke. replaced that and so far, has now shut off at the ignition 3x now. like old times...wooo
now, the next question please: the solenoid rubber boot on the wire end includes a "tube" about 1.5 inches long at 90 deg to the body. The old solenoid, this was full of crud/dirt. So - is it correct to assume that this does NOT connect to any thing? Is it a breathing or heat dissipation tube or ?