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Correct packing size for our 1991 P42 is 3/16, which came with the standard bronze type box. I use the PTFE material as it is less prone to friction and seems to do a better job preventing sea water passing by the packing material. Ours was last done in 2011 and will do it again next year (2018) when I haul the boat to redo the bottom. Some pointers that seem to work for me:

1. Service wrenches of the correct size have worked best. https://www.bing.com/shop?q=service... and originIGUID=D4AED6A013D7462BB7A81BB93811C90B Different sizes for the box and lock nut; one is 2 and the other 2-1/16th as I recall. Measure to be sure. I also picked up two pieces of scrap SS tubing that slides onto the handle for additional leverage. Pipe, adjustable and related type wrenches have not worked very well because of the limited working space.

2. Difficult to get the old material out due to the cramped engine room quarters. A dental pick has worked in the past, or a long small diameter wood screw.

3. Install one ring at a time, press it back with the box then back it off and put the second ring on, and so forth. Three rings work.

4. Apply a liberal amount of anti-sieze compound (local auto supply store) to the threads and where the lock nut face touches the box.

5. Once installed, hand tighten, then check it again after a few hours of run time after the new material has had a chance to settle in.

Some say you can do it with the boat in the water, but I do mine while out. PITA regardless.