why is my Bosch GSB VE2LI drill getting slower (its not the battery)?

You say you have two of these which suggests that you do a lot of drilling - needing to have two - and presumably you use them to do different work - not needing to change the tool.

You suggest but do not say specifically that only one of them has developed slowness.

Brush wear might be a factor and so might environment - your work might create dust contamination that's getting inside - possibly gumming up the bearings or the commutator.

But....
In the UK Amazon sell brushes for this model £1.69 + £3.99 delivery.

Good luck...

Peccavi
April 2013