Bellows aging is certainly an issue. Storing with the outdrive lowered may be easier on the three rubber bellows but there are also other advantages too with leaving her down.
From the Boat US site regarding sterndrive storage....
"...when it comes to storing your sterndrive, it's important to prevent water from entering the exhaust hub of the propeller. Openings that are designed to let the exhaust out can also allow rainwater and snowmelt in. Water will accumulate in the unit's housing if the drive is stored in the "up" position. In cold weather, any accumulated water in the sterndrive can freeze and, under the right conditions, ice may expand and crack the housing. When putting your boat away for the season, store the sterndrive in the "down" position or use a sturdy, waterproof cover over the prop to prevent water accumulation in the housing."
We pull our boat out of storage in mid April and the north east freezing temps can still wreak havoc if conditions are right.
Since YMMV with stern-drive storage experience, here are some facts to help with knowledge and storage for those inquisitive minds on the site....
Sterndrive care and Feeding
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