Resetting Winter Vario to Zero?

I have a Winter variometer that works great except that at rest it
reads high (+1.5). While that makes me feel good in flight, I'd rather
zero the thing out. The question is how to do this.

I have been told two different ways to do this;

1) Find the zero adjustment - I removed the face plate but cannot find
the adjustment. Any ideas?

2) One person mentioned that over time the needle looses weight.
Because these devices are so sensitive the needle reads high. The idea
then is to add back the lost weight. This person recommended a small
dab of finger nail polish.

The last choice is to send it back to the factory which I would rather
avoid.

Thanks.