Before there was Seal Mate there was the Feeler Gauge, although if you choose a gauge that was too small you could cut the seal with the sharp edge, I remember my dad doing my bike 45 years ago with a set of feeler gauges.
I have had good results by changing from fork oil to ATF.
About 15 years ago KTM were having a lot of trouble with leaking seals, it turned out they were too tight and the seal was rolling, the problem was fixed by going to looser seals not tighter as they had been moving toward.
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.