My, almost completely seized up, Universal Heliar has come back to me to-day. I promised, a long time ago, to have a go at fixing this problem and post photos and description. I understand there are a number of owners who have similar, if quite not so acute, problems.
This is also of relevance for cleaning the inside middle bi-concave lens and the insides of the other lenses.
I think that Voigtländer has changed the location of the only lock screw during the long life of the Universal. Tim Deming mentioned that his was hidden underneath the broad aperture ring. Mine wasn't - it was only screw in the side of the barrel in front of the aperture ring.
I should also explain that mine is a pre-Universal engraved type - before Voigtländer decided on the Universal name. I have no reason to believe that the mechanism was changed when they decided to make it a standard product.
I would label this a ** level difficulty job.
** means that it can done on a kitchen table with good lighting with ordinary tools at one session. Knowledge of clockwise/anticlockwise is required as well as a container (soup dish?) for the 3 small screws and a soft cover to the table. The Heliar is very well put together and the problem with friction in the turning system doesn't mean that the screws are going to be difficult. Remember this one is older than almost everyone else's Heliar!
The first photo shows Heliar. The second shows the aperture ring removed (just a single screw which goes down to a rather concealed hole/thread in the aperture disc) and the locking screw (central in the photo) for the front/lens assembly. Note that this screw is fortunately steel - otherwise we would have a rash of total failures with severed brass screws. When this is removed, the front assembly can be unscrewed from the front -the last photo.