How to tell if a lifter is bad. i hear a tapping after it warms up on the passanger side

SOURCE: what would make my lifters tap

It sounds like tired hydralic lifters to me. If the noise was constant it would be a worn out oil pump instead

SOURCE: Hearing a tapping noise from the lifters.

Have your oil pressure checked with a reliable mechanical gauge. If pressure is good, change oil and add a pint of marvel oil: it will help clean insides of lifters. if noise persists after a couple of weeks or gets worse, you will need to change lifter(s) check cam and rocker arm for wear.
Your rockers are shaft mounted and are not adjustable.
Hope this helped you and the problem does not turn out to be a serious one!
good luck

SOURCE: bad valve cover gasket, misfire and tapping lifter.

what do you mean with 'bad valve cover' ?I asume it is leaking oil.it means that the rubber seal is not sealing anymore,it has gone hard.tighten the cover bolts sometimes seals it for a while.to get to the rubber seals the inlet manifold has to be unbolted and moved,a fairly involved procedure but easy to do if you have a manual and standard handtools.The misfiring is likely stray arching of the coils .remove the top plastic cover of the motor andlook when it is very dark [like lightsof in your garage] and look for sparking.If so ,replace sparkplugs or/and leads.[remove inlet manifold also]Tapping lifter,works with oil,try engine oil flush and/or change oil brande.if problem persist replace lifter,lifter undervalve cover

SOURCE: 320 SLK Coil ticking.

I also have a 2001 SLK 320 with same issue. It is definitely a lifter problem due to the fact that it is occasional. Also, if a coil were bad then it would trigger an engine code ('check engine' light), plus it would run rough for longer. Try some oil treatment first, if that does not work for you then you'd have to replace the lifters.
Honestly, it's a lot of work. I am not sure if I am going to keep it or not. I honestly absolutely love my car but I just don't know now.

SOURCE: tapping noise like a bad lifter Replaced lifters,

one guy is right,it could be a vauxhall tap,even new vauxhall cars do the same.but lets be serious?to calm this and slow down the noise,get the tappeds checked out .it will need the cover removed and with engine running feeler gauges placed between tappeds it will revel one tapped loose and can be fixed within a couple of secnds.adrian,,,