I also have a 1999 Kawasaki 1500 Vulcan Nomad (with 145,000 klm's) . I was told by a Amsoil rep , that Amsoil was the ONLY oil that you DON"T change before you store your wheels for the winter . That's about six mounts here in CANADA . What are your thoughts on this ??
I sell Amsoil. And I would say this answer from the Amsoil rep is patently false. Lubricants have come a long way in the last few decades. Horsepower per cubic inch has gone way up, increasing internal pressures on components. More and more close tolerance hydraulic valves and solenoid components are used in today's engines that require very good lubricants to function properly. Not to mention, internal temperatures have risen as well. Lubricants have done a great job keeping up with the ever increasing demands that these engines place on motor oil.
This rule of thumb to change oil before storage came from the days when it was imperative to prevent internal damage. However, this is no longer as true as it used to be. Though motor oil is not naturally able to prevent rust or corrosion. More than adequate protection can be engineered into a lubricant. I do not have a list of which oils will protect an engine in storage. But Amsoil is not alone in this. There are others.
Amsoil describes a bit of what I am talking about. This statement refers to their 20w-50 MFC (motorcycle) oil. Other than viscosity, this is pretty much identical to the 10w-40 Amsoil I sell to Spyder owners. Interestingly, this Amsoil statement does not claim to be the only oil with rust prohibiters. And by inference, meaning a pre-storage oil change is not necessary
Motorcycles are prone to rust from storage, humidity and short drives. Rust can cause major damage such as roller bearing failure, uncontrolled wear, compression loss and blow-by. Good rust protection, however, comes by design and is not natural to engine oils. Unlike many motorcycle oils, AMSOIL MCV contains special anti-rust agents. It passes the ASTM D-1748 humidity cabinet rust test and clearly demonstrates superior rust protection (see photos below).

Amsoil -------------------------------Castrol
The one thing I do not like about some of Amsoil's test results (this one as example) is that they do not always provide enough information about the competitors lubricant to be sure we are seeing an Apples to Apples comparison. This, to me, is a bit suspicious. Like cherry picking the results. As an Amsoil dealer, I know there is a good deal of skepticism about Amsoil products. And I think this kind of 'Test' result adds to customer doubts. So I post this more as a response to the OP's question than as any sales pitch for Amsoil. I don't mind being honest about Amsoil. Or any other product I carry. You don't want to buy 'Snake Oil'. And I don't want to sell Snake Oil.
If you would like to view the entire article you can see it here.
http://www.harley-performance.com/amsoil-mcv.html
I will say this. I let my Spyder sit for over 2 years, maybe closer to 3 years, with the same Amsoil which already had over 5,300 miles on it when I parked it. I know, I could be turned in for Spyder abuse! And I am not recommending anyone do this! But to make a point about Amsoil. I put another 500 miles or so on that old oil when I finally got my Spyder running again, and had it analyzed by BlackStone Labs. The results were great and virtually identical to previous test results. Rust or damage to metal parts would definitely be reflected if present. So, to me, this verifies that Amsoil is doing the job. But not that other oils will not do as well. Though, as demonstrated in the pictures above. Not all oils will give this level of protection.
Browsing around the Internet for information on this I stumbled upon this independent video comparing Amsoil to Royal Purple (which is a very good lubricant). I've watched several videos by this guy on a variety of products. It is a bit long. I think he does this to verify that he isn't cutting corners or biasing the results. But you can skip through using the slide bar to the results along the way. I thought it was pretty interesting.
https://www.youtube.com/watch?v=E2zS8MyvJxU