In July 1980 I purchased a new Regal boat with a Volvo Penta AQ271DP outdrive. The outdrive suddenly doesn't stay up while parked and and wil not maintane a trim setting under power. About as fast as I trim it to zero under power it trims itself back to minus8. There are no visible fluid leaks. I'm having trouble identifying the outdrive. I know the "271" refers to the horsepower of the Chev V8 and DP designates duoprop. How do I determine the outdrive model for parts and troubleshooting? Model number on the tag 888130 serial 1101557567. These stamped numbers are not totally clear, model almost looks like 86S130. A local marina says I need new cylinders which require an expensive kit for installation. To me it seems more like a check valve or pump.
Any ideas or suggestions? I appreciate the help. thank you.