The best thing to do is replace the trim assm. stop trying to figure it out. The problem is in the valvebody of the unit. Have never seen anyone fix them, have seen alot try. Most of the time what happens is there are steel check balls in an aluminum body, and after awhile the steel balls miss shape the seats they set and seal in. In other words the steel beats up the aluminum sealing surface. Merc at one time made a replacment kit,,dont know if still avalible. If not Cook CMC makes a tilt bracket that will also give you 5-6inches of setback {like jack plate} which may improve overall performance to-boot. Cary
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Call & Arrange your powerhead re-build today! I can work with trade-ins & I'll give you more for your core! Need a boat mechanic to come to you? I'm a Mobile Marine Tech. also. Call & schedule today! 281-312-9856