Well installed the progressive springs today. Drained the oil all looked good and refilled with ATF fluid as per the service manual. Manual said 377CC right fork and 372 CC left fork. Took it out for a quick test ride and what a difference it made.
Must agree with the last two posts, there is oil made specifically for forks and it comes in various viscosities. I've not done anything on my Wing forks but replaced many fork seals on our dirt bikes and use the correct fork oil.
The manual says ATF oil in the forks, progressive says 15W oil, I live in the middle of nowhere and no fork oil available, so I used what I had, once I get some 15 weight oil probably change it, but for now that's all I had.
But I can tell a huge difference with the progressive springs.
I just changed the fork oil in my 88. Honda called for ATF. I have progressive springs. ATF is not heavy enough. When I hit a bump in the road the front end will bottom out. Did not know what weight to put in with the progressive springs, so thanks HALLCT for that info!! Honda called for 10 w in the 89. I will try the 15W as that is what Progressive called for.