My rear shock on the 650 had seen its last day after about 28,000 miles. The back end softened up considerably and making adjustments at the knob made no difference. Of course, the dirt sticking to the leaked fluid also helped. But, by the time the fluid started leaking, the shock was already gone since there was no pressure left in it anyway.
So, basically, you will notice the back end get softer and not give you the same feedback as it did not long before. Keep in mind, your shock will break down gradually as well, just frrom good hard riding. But, when it makes a dramatic change in a matter of a short period of time, a week if riding every day for example (or faster), then you probably do not have much life left in the shock.
I took mine to the local Ducati dealer since they have the best mechanic around, and he has A LOT of experience with suspension, and decided to replace the shock with a new Penske. The new shock is great, but honestly, the performance is better than new, but not as much as expected. Not because the Penske is a bad shock, but because the stock shock is not that bad for this bike off the floor. Granted it is a bit soft, but what do you expect on a bike made for what the little stromboni is built for?
Once you get the old shock off, you can definately see the difference between ANY decent shock, and the stock unit. The stock shock is pretty weak and definately NOT intended to be rebuilt. I did have mine rebuilt to get me through a trip until the new shock arrived. nevertheless, it did not hold out well.
In order to rebuild the stock shock, it will need to be drilled out and have a valve put in. There is not much room for this on top of the stock unit, and I do not recommend it since the shock housing is round on top, and makes it VERY difficult to make a good seal with a valve up there.
Anyway, I like the Penske and its adjustability. It is also a rebuildable unit that is MUCH better built than the stock shock. It will last longer, not need replaciing, and does the job better than the stock unit.
Getting the right size is tough. The wee strom is not a standard size shock, but I think it may be the same size as one of the older bandits??? if I remember correctly. Your dealer may be able to help you out on this one.
I also have a Fox shock on my race SV that I have been very impressed with. It is a great shock and does the job very well. Fox does not make shocks anymore, so finding the one you need, without the help of a dealer or rep to call may be tough.
Hope you found something good in all of this. Good luck and let us know how it comes out.