1996 volvo penta 5.0 gipbycce. Pulled the engine (I'll spare the details) and am in the process of puting it back together. I only want to do this once so I want to make sure all my bases are covered. Looking in the lower exhaust there are flapper valves. They do not move freely (boat has been sitting for a decade!) so I was looking to replace them. Upon research I found a bulletin that states that after further testing volvo has determined those flapper valve are no longer needed and to discard them when they stop functioning... no problem. However I have also noted that they have changed the risers from 8" to 11". So my question is are the valves no longer needed because of the increased height in the risers? Should I just try to free up the flapper valves and still use them? Or should I God forbid just buy the newer risers... I may have to anyway. I haven't checked inside those yet for corrosion. Thanks in advance.