masking on Al base parts for EN

Recently, customer required that plated Al parts with EN, Somewhere have to be masked, we've tried couples masking paints, however, they were melted since high temperature(88-94deg.C) and longer plating time(3-4hrs.).

Some are hard to cohered.

We've tried Epoxy too, however, it hard to be removed.

We are looking for good painting material for that purpose.

Thanks!