I had my girlfriend's driver in the garage last winter for a few days with the front struts fully extended. This is an '89 740. When I put the car back on the floor, the driver's side strut remained fully extended. This problem went away as soon as it got above freezing. The struts still damp well enough that I wouldn't replace otherwise, though I'd prefer they not re-freeze next winter. Might the water in the strut dissipate over the summer and fall? Or is this certainly going to be a problem again when it gets below freezing next winter? Thanks for any input.

Probably not a water issue but visccosity of the hydraulic fluid. During normal use, there is tremendous amount of heat built up inside the strut which will evaporate any water which may be present.
I would think that the strut being hyper extended was not "frozen" but extended beyond its capacity. Normally, a hard shove will bring the shock back down.

Klaus
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Please answer, we need to know if the advice is good or bad. The 164 has a new home, all I am left with are 2 turbos :)

How cold was it? It seems unlikely much water could be inside - how it would get there? I have had very stiff struts particularly on Japanese cars when the temperature went down below 5F or so. They seemed to relax on use or as the temp rose during the day.