Volvo Penta 8.1 2006 Compression Question

On our 4160, 600 hours = PORT= Compression: 145-152 , STBD = Compression: 146-154
All cylinders should be within 5% of each other. Putting stuff in gas wont likely fix anything, suggest your get cylinder leak down test to determine if piston rings or valve faces /valve seats. 175 way too high, 125 way too low!
Get oil sample from engines and send for analysis, will tell you what might be wearing. Is there records of maintenance done on engines? Get compression test re done and what were reading on port engine? Yes, could be $$$ problem depending on cause. Dont walk away but get tests and then make a counter offer! Rebuilt 8.1 VP engine $9400 + R+R. Get codes read from engine ECU to see if any overheat, low oil PSI, etc, that info will help diagnose other problems. Good luck!