Old M rangefinders

[cmiller@berkshire.net (Curt Miller)]

Hello,

        I'm receiving a late M3 DS on approval today from a very well
respected dealer.  I've considered it awhile for use as backup and for long
lens work.  While discussing the condition (listed as 9+) with the
salesperson, I asked if there was any sign of separation in the rangefinder.
He indicated that he didn't know how to tell so I told him to look in
through the largest window from the front of the camera to see if he could
see a faint oil-slick type of line circumscribing the front of the
rangefinder prism.  He indicated that he could see about 1mm to 1 1/2mm
line.  The range-/viewfinder image, however, is clear and bright.  I know
this is a very common problem among the older cameras and is frequently
overlooked but, since the only repair I know of is to have Leica replace the
rangefinder unit with a rebuilt one (for $500), it is a problem to consider
carefully.

        My questions are: 1) how much separation is acceptable,  2) how fast
does the separation advance in normal household storage, and 3) is there an
alternative repair/replacement solution to Leica's $500 exchange of the
entire unit?

TIA

Curt