I just spent some serious time trying to figure out why my bike has been so stiff after getting new fork seals and fork oil replaced. I also had it lowered front and rear. The ride was so stiff I couldn't barely stand it. Not knowing what the problem was, I raised it back up, tried adjusting the suspension and ended up having to replace a fork seal and fork cap in the process. Each time sticking with the 10W fork oil. After all of this, the suspension was still very stiff. One dealer called Suzuki tech support for me and they told him there was 2 equivalents/recommendations for the Suzuki L01 fork oil. 1) Bel-Ray HVI Racing suspension oil 5W or 2) Spectro 125/150 cartridge fork oil.
Not having either of those in stock anywhere that I could quickly find, I used Bel-Ray 5W fork oil. This fixed my problem! I don't know how anyone could use the 10W at all!!!