My comments are based on the Leicaflex SL & SL2, but AFAIK should hold true for the Leicaflex original.

The original battery would be the mercury PX625, but the ones you tried should definitely make the meter work almost accurately (alkaline) or very accurately (Wein).

Just in case, the meter is switched on only when the advance lever is distanced from the body (advanced about 10 or so).

Also check the battery chamber contacts for dirt, oxidation, corrosion, etc. Clean as necessary. See if the battery contacts are flattened or otherwise damaged.
If all the above tips fail, then your meter is broken... :-(

Don't give up - it's a wonderful camera!
(if you want a 90mm f/2.8 for it, see the classifieds here)