It might be worth a bleeding top off with some Fork oil?I'm pretty confident that the stock one ON the bike isn't doing much anymore after 25 years...
On my K5- the OEM actually worked by simply taking it off, bleeding the air out, and topping it off with fork oil.
HUGE improvment. I didn't even change all the oil out!
However there were no signs of it leaking any oil either.
Over the more than a decade, I guess small amounts of air get in there over time,
it cause the first 1-2 cm of movement to be 'un dampened'
that first 1-2 cm of travel of the damper IS where it needs to do most of it's dampening however in most cases.
Just my 2 cents.