If the buckets are noisy then check for wear on them with wooden rod (mixing them up - swapping in holes - will cause camshaft damage - its guaranteed)
If any tappets are soft after hot shutdown, they are bad, if you think your tappets have been swapped around them you need to check each tappet on a perfectly flat piece of glass, they should be slightly domed - if they are flat you will destroy the cam and also the lifter as to function correctly it must rotate in its bore, otherwise it will sieze and cause serious damage.
Engines with such valve system should never use thick engine oil.