Rob:
My experience with the SP III (70,000 km's over two summers) was that I could solve the glare problem pretty easily by tweaking the
contrast level - about one colour bar to the left, if I remember correctly - and by very slightly adjusting the tilt of the GPSR on the motorcycle. I have never needed to use a glareshield with my SP III.
I'm not sure how your GPSR is mounted, if you have a "fixed" type mount that does not allow for vertical angle adjustment, or if you have a Ram-Mount or similar that does allow for vertical adjustment. I have a Ram-Mount with an arm about 3 inches long that attaches to the back of the Garmin SP III bracket. You can see a picture of it at this link:
SP III Mounts. Whenever glare has been a problem (e.g. sun shining from behind me), I just adjust the tilt a few degrees - not very much at all - and this solves the problem.
The second summer I was riding, I screwed up the screen cover very badly by cleaning it with an aircraft window polish. The screen had a few minor scratches on it, and I wanted to get rid of them. Well, I got rid of them OK, but I also removed the quarter wave dichroic coating that Garmin applies to the surface of the screen (actually, to the plastic cover that goes over the screen) in order to reduce glare. The thing was practically unreadable in sunlight after that.
I sent the unit to Garmin in the UK for repair (via a dealer here in Switzerland), and they replaced the whole front case cover for me. The screen cover is plastic-welded to the front case cover. Total cost was about CHF 50 (about GBP 25, I think) and the turnaround time was a week. Getting the SP III back with a new screen cover with an un-damaged coating on it was like getting a whole new unit.
So, I suggest you check - compare your SP III to a new one in a showroom - and see if the 1/4 wave coating has been removed or damaged. If so, get the front cover replaced, it is well worth the expense.
You might also want to try doing a "factory reset" on the settings of your SP III. To do this, first, save all your waypoints, routes and your track logs by uploading them to MapSource (the factory reset will erase all your waypoints, routes and track logs). Then, with the unit turned OFF, press and hold the QUIT, ROUTE and RIGHT PAN buttons. Press and release the POWER button one time. Then, release the RIGHT PAN button only. Continue to hold QUIT and ROUTE for approx 15 seconds. During this time, you should see a blank, backlit screen. If you see this, then you know that the unit is resetting. This will reset the unit to factory defaults for EVERYTHING. You can then try moving the contrast slider one 'colour bar notch' to the right (I think this is the correct direction) or to the left and seeing if that makes it easier to read.
By the way, to anyone else reading this, don't do this factory reset sequence unless you have a reason to. Not sure why not, but that is what I have been told - "don't do it unless you need to".
PanEuropean