FWIW ;
Before you go tearing the SLS apart , take the time to clean out the oil reservoir .
I discovered some boob had filled mine with ATF at one point and the bottom was still 1/4" thick with nasty looking slimy dirty grimy crud
.
It was a seriously fiddly job to clean it all out , then I replaced the filter and replenished it with the correct oil and it works fine .
As soon as the oil turns dark again (it uses a clear Mineral based oil) I'll go back in and clean it out again .
Oil and sweat are *MUCH* cheaper and easier than rebuilding the leveling valve , replacing the spheres and so on .