Pearson 365 and 367

My shower taps are getting more difficult to close and I was looking to replace O rings, but I cannot determine how the plastic knobs come off.  I have tried both usual ways a) if the top of the plastic knob separates to expose the inside or b) if the entire plastic knob comes off to no avail.  I have tried as hard as I dare and don't want to break anything.   I cannot tell for sure if this is the original equipment, but it sure looks like it could be.   Can anyone tell me if the system is meant to replace an O ring or that the entire unit has to be tossed and replaced with new?

I was able to open the drain plug and let out the oil.  It was very messy and I wouldn't do it again:  you still do not get all the oil out because of the angle of the engine and the placement of the plug.   It was very difficult getting the plug back in place too.  I have a vaccuum pump and I am going to remove the valve cover and see if I can access the back of oil pan from one of the oil gangways on the head.  I plan to measure out the length of tube against the engine first and mark it before I insert the tube down to know that I'm in the pan. 

I want to thank all the members who provided help and advice regarding the removal of the Westerbeke engine from my boat.   It was a sad day when I discovered my engine was seized tighter than a drum because seawater made its way through the exhaust system back into the engine.   The source of the problem being the "loop" in the exhaust system as specified by the marine surveyor to prevent a following sea pushing water into the engine while sailing.   The loop was higher than it should have been.  The salt water had been sitting in my engine for nearly 5 months.  Nearly 4 liters of salt water had mixed with oil and run in the engine.  I extracted 9 liters of this grey mixture from the oil pan!
A mechanic who told me he has "saved"  3 seized engines said I should spray a penetrating oil called Moovit into the cylinders and let it sit for 24 to 48 hours and then gently work the shaft from the transmission (the Paragon beast) by hand back and forth.  He told me I had nothing to lose and there was a good chance the engine would run again.   After 48 hours I was able to get 3/4 of a turn on the engine before it locked up again and the clutch slipped.   I spoke with another mechanic who figured the source of the problem now maybe a stuck valve.   Again I sprayed the Moovit into the valves, although I know the seals were going to prevent the penetrating oil from getting in.  I let it sit overnight and the next day removed the rocker arm assembly with a mechanic.   He checked the pushrods then he pressed on each valve spring to ensure the valves were moving.   He told me to hit the start button:  she spun over twice, fired up and ran as smooth as if nothing had ever happened. 
Several oil changes are necessary to remove the dirty oil from the engine but compared to the cost of removing, rebuilding or replacing an engine.....  My costs: Moovit $22,  10 litres of oil $26,  2 oil filters $11. 
Yes, I know I dodged a bullet here.   

I need to rebuild the beast.  Can anyone provide me some step by step guidance as to the best way to get the beast out?  What needs to be removed to create enough clearance etc?

Thanks for all the help and advice.  Experience is a great teacher and learning from those who have faced these issues successfully with the Pearson is a real asset.  I have a lot more to learn about her to maintain her properly.   If any of you have some pieces of wisdom to share on what you've learned from maintaining your boat, please pass that on.

If any one has a used or rebuilt raw water pump and or a Paragon transmission I am interested in buying.  If you have suggestions as for reasonably priced alternatives, I'm all ears.  From reading the posts, its seems that the 1:1 Velvet Drive is a popular substitute for the Paragon.  Creative suggestions for the water pump? I'm going to get mine rebuilt but I'd like a back up.   I got a price quote for a new one from a Westerbeke distributor and I think gold is less expensive.

I'm looking at buying a good used Paragon transmission rather than rebuilding my existing one this fall.  If you have one for sale let me know.
Thnx