Does it tilt after you sit on it again, or does it tilt as you tighten it?

Mine tilts as I tighten it down on the rails of my Serfas. Starts off perfect, ends up wonky. So I have to guess how far off it will be, and then start tightening it with a compensating tilt. And swear a lot. Bad words help.

Problem with mine is that once it starts tilting, it's already too tight for me to just flatten it out. I have to loosen the bolt again.... which changes everything... bad words.

Recycled Cycles has a ton of used seatposts if you decide you need to replace yours for a better fit. Sammamish Valley Cycles (redmond) has a couple bikes for sale with Brooks saddles. (didn't see any Brooks for sale, though). They might know how to make one fit the seat post better. SVC also has Ibex!