I vote for air in the lines.

When recently flushing the (totally stock) brake system in my '84 190E rally car using gravity bleeding, I didn't initially see that there was a divider in the master-cylinder reservoir that was preventing fluid from getting to the rear section and didn't realize I was allowing it to run dry. I'm not sure what kind of bleeder you've been using, but this might be a possibility.

By the way, RC Imports did the suspension and differential mods to this car and they REALLY know what they're doing - I highly recommend them.

Best Regards,
Rob

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Robert Fini

'12 ML350 BlueTec, 111k
'06 E320CDI (x2)
'05 T1N Sprinter 2500/Pleasure-Way Plateau TS, 72k
'97 C36AMG, 325k (son's)
'94 E320T, 249k
'93 190E Sportline LE, 168k (daughter's)
'84 190E-2.3/5spd (Stage Rally Racer)
'66 230 W110 Sedan (Barn Find, Vintage Racer build in progress)