You should be able to drain most of it if you have'nt moved the machine and mixed the oil with the water, but it's cheap insurance to change the oil anyways as the crown and pinion are the high wear item in those diffs. I've read alot of stuff about the water and those on this forum and I have had a 1974 sv300 for years (like 15) and long ago talked to the old mechanics from the local ski hills that worked on them and the way to fix the problem is to isolate the cyls from the lid . If you build a cross member that the cyls can push on the lid will stay sealed. Worked for me