loss of brilliance

[Axel Weiss]

Hello everybody,
after listening John Patitucci's first CD and Al Jarreau's "Hearts Horizon" in 1988 I was totally convinced and overwhelmed by the Smith tone. Immediately I bought a BT6 (3 knobber, mahagony core, Koa top), the only available in Germany at that time and I'm still playing that instrument.
In particular I love that brilliant "click" in the higher frequency range while striking the strings of Smith basses.
However, I've got a notion that brilliance of the bass has decreased advanced in years ?! Any idea what could be the cause ? Meanwhile the polepieces are rusted a little, have been adjusted for several times and are not in factory setting anymore. Apart from that the bass is in good condition.