There is a cross-reference to a Honda car (late 90s Civic I think) t-stat that will fit the ST1100. Since there are a lot more Civics than STs around Stant and several other aftermarket companies make t-stats to fit. Someone here can probably produce the Stant part number.
One can buy "fail-safe" type t-stats for many cars, maybe they are available for the late 90s Civic too. MotoRad (http://www.motoradusa.com/index.html) makes these fail safe ones. I looked up the number for a '98-'99 Civic Ex and got this:
Fail Safe Thermostat 7328-170 170 degree. O.E. Recommended Temperature
You'll want to confirm whether this is the car and engine the ST1100 shares a t-stat with to be sure first.
A fail open thermostat does exzctly what is says. When it fails it stays open to continue to allow coolant to circulate and cool your engine. A normal thermostat failes closed and stops the coolant from circulationg to the radiator then your enginge overheats. Aluminum engine overheats you get warped heads and all sorts of other nasty stuff. I've been fortunate to experience the overheating one time and got rid of the vehicle before it was too late. The overheating was from a different problem in that case though.
Sticking open seems to be what the Honda thermostat does anyway. I've not seen a mention of one sticking closed.
I'm in the process of installing a st thermostat that I bought from Turbo City. It's made by MotoRad, an outfit that makes parts for BMW.
I'll keep my Freedom, Guns and Money, you can keep the "CHANGE"
I know of one case (Jon Ransom's '91 ST11) where the t-stat failed at least mostly closed. According to Jon's photos it appears to be because the strut that the wax motor pushes against to open the valve corroded through and broke.
On the 1100, at least, they can definately fail closed. It happened to me out in the middle of Oregon returning from WeSToc up in Idaho and I blew one of the coolant hoses that goes to the heads. What a hassle. The part of the thermostat actually fractured off and the thingy that pulls the valve open against the spring then no longer had a grip on it. Coolant flow kept it in place, though, plugging the only hole (besides the bypass hole) that coolant could flow through. After the hose blew and I shut the motor down, the "thingy" dropped away and down, exposing a hole in the middle of the valve and though I didn't discover this problem until after I got home, it did allow enough coolant flow to get me home.