Weak Return to Center

I just refreshed my suspension after 100k miles on my 2005 325iT. I replaced shocks/Struts (Koni FSD), control arms (Meyle), bushings, shock mounts, etc. I had an alignment done by a very good shop and everything is drives great except the steering does not return to center like it did originally. I had the shop double check the alignment and the suspension and everything is as it should be. I can only guess that the new control arms, shocks or something is slightly different from the original factory design and I lost some caster in the front end. Anyone else ever have this problem? Got any ideas on how to fix it, since caster is not adjustable? Should I invest in some camber/castor plates?

Thanks.

Erich