My 1967 hydro swift boat has worked great for the last 4 season. Last year I decided to have the motor tuned up at a local boat shop. Ever sense the motor will not engage in forward or reverse with out stalling, even out of the water. The motor runs and idols great, and compression is good. When the LU is engaged it instantly comes to an abrupt stop and stalls out. I had a boat mechanic/friend look at it he believes the solenoid is engaging in forward and reverse. After he ran the motor and did a couple inspections. He's sure the issue is in the LU. Could the wrong oil or water in the lower unit cause the solenoid to short out on both reverse and forward circuits at the same time? Is the issue mechanical ? Please help if any one has had to deal with this issue or may have some input as were to look next? Thanks in advance.