If the shim isn't perfectly square, might it damage the valve or cause galling or wear? Also, how critical is the factory surface?
When Suzuki introduced the RMZ250K4 they gave this warning about the shims on that model-
Forged, 7.5 mm OD tappet shims.
Selection range: 2.50 - 3.50 mm.
To prevent damage to the surface treatment
at the top surface of the valve stem, only
use tappet shims specified for the RM-Z250.
If the surface treatment is damaged, the
valve will fail. Do not use 7.5 mm OD sintered
metal shims that are available from
the aftermarket or specified for some
Kawasaki models. Do not use 7.5 mm OD
forged shims specified for GSX-R models
as the surface finish is slightly different and
the adjustment range is not suitable (1.20 -
Now I have never seen a warning for the DL shims, but why risk damaging the top end to save a few bucks? I'm not saying that I know what the valve/shim surface treatment is, I'm saying that because I DON"T KNOW I would rather not take the chance......Once surface hardening is damaged a part fails incredibly quickly.
If it's in the specified range, leave it alone, if you need a shim, just by one. I mean you are only doing it every 20000 kms anyway....