The most probably cause of a gear crank handle to transmission body leak is overfilling of the transmission. The transmission should be filled with the specified gear lube just to the point of the base of the worm gear of the crank picking up gear lube. A simple solution to finding an overfilled transmission could be a turkey baster with a piece of vinyl tubing on the end of it to extract the excess.

HERE is a link to a gear lube discussion for the motor and the transmission.

However, sometimes, the decades old 1940's technology nitrile rubber o-rings are the cause which may have been in service since the airplane came from the factory.

Here is a solution posted by Beech Lister Kevin O. for his leaking Gear Crank Handle:

1. Cut safety wire remove three screws place rag under assembly to catch any dripping oil tap on assembly to break it lose from gear box place small rag in hole where handle came off--this keeps oil from draining out remove screw from handle slip shaft out from other side remove O-ring (AN6227-9) clean all parts and inspect shaft for damage on end. Also, before removing the crank handle housing, match mark one ear so that you put it back exactly in the same orientation as it came off. This assumes that it has been correctly installed previously. Note the slight cant upward of this handle HERE.

2.  Here is a picture of the groove for the O-ring do NOT scar it getting the old O-ring out. After cleaning all the parts, slip in a new O-ring, AN6227-9 or MS28775-111, using a small wooden dowel to help in placement replace the washer and spring, lube shaft and slowly insert into housing.

3. Place shims on shaft while pushing in on shaft--place handle and insert screw and nut.

4. Place some RTV around housing face that fits to gear box housing/assembly, place handle assembly onto gear box--making sure that it is pointed upwards--NOT down (this is why you match marked it at the beginning).

5. Replace screws and safety wire all three -- note the slight upward angle of the handle in the above photo on the left.

6. Test to make sure the handle engages the gear box properly then place cover back on spar-- making sure the handle is not caught under the cover.

7. You may want to consider leveling the aircraft to insure that your oil level in the transmission is properly filled. Place a cookie tray or rags under the handle area to catch any overfill that may be in the transmission housing.