You may have covered this, but have you been buying OEM fork seals or aftermarket?
If the latter, try the OEM, there's a chance it could fix your issue with the seals
My 2000 model is still on the original fork seals but one started weeping last year. I have a little trail bike and that’s also suffered in the past so I got a seal doctor tool (£15 on eBay) which worked brilliantly. It won’t fit the GS stanchion though, so I got a seal buddy tool (£3 on eBay) and that has also worked perfectly.

