I have replaced the lifters on my '85 Westy and  I still get  noise from
time to time.  I have tried Marvel's Mystery Oil.  It may help some, but I
think it thins the oil some and my oil pressure is low enough,  thank you.
Some have said it depends on where the cam stops when you shut it down.
This would explain the random nature of the problem.  I have my lifters
adjusted at 1 turn, splitting the difference between the Bentley ( 2 turns)
and Boston Bob's (0 lash) settings.   I hate to go tighter than 1 turn,
because the lifters do eventually quiet, and I certainly don't want to be
too tight and burn a valve.  When the valves are quiet, the engine runs
good.  When they are clacking, the idle "hunts" a little, often sitting
just above the normal speed.  Last night I changed oil (Valvoline 20-50 and
Mann filter), and the valves were clacking away.  They would not quiet a
idle, even after 5 or 10 minutes.  They only quieted down after a test run
where I was able to run the engine up through the rpms.  Then, voila, peace
and quiet.
Because I have new lifters, can I run 2 turns?  I really don't feel like
re-adjusting all the valves, checking compression and then maybe having to
do it all over again.   How in the world can you run "0 lash"?  You must
get some noise all the time.  I thought the 2 turns just pre-loaded the
lifter and would not actually open the valve.  Is the 0 lash for old
crapped up lifters?

                                         Jay  '85 Westy (the Hindenburg)
                                         Enjoy the ride before she blows...