1997 90HP Evinrude T/T.

This motor is in very nice condition and has not been in the water for3-4 years. However I have serviced it every spring and tested it in the barrel every 4 months. Last service and test was in May and everything was good. Pulled it out for testing yesterday and found that the T/T worked fine in the up condition but although the pump appears to be running in the down condition it does not appear to be pumping oil and sounds like it is full of air and will not come down. Lowered the motor as far as the Trim cylinders will allow, they being fully extended and not moving, using the manual valve. Raised the motor and filled T/T with oil and repeated the action. no change. Ran the T/T direct from a battery, no change. Noted that with the motor up and the manual valve backed out, pressing the up button results in rapid down movement until the motor reaches the extended Trim cylinders and then stops.
If anyone has any thoughts on this please respond.
Thanks.

Apparently no one has any thoughts on this so maybe this will help someone else. Filled the reservoir with ATF and backed out the manual release valve 1 1/2 turns. left it overnight in the up position. Closed off the manual release this morning and the system works again. topped off the fluid and cycled a few times. Topped off again and all is well.