Replacing hydraulic valve lifters W124

[300TDT]

I've had a worsening rattle/ticking from the top end of my 220,000 mile W124 diesel for 5,000 miles or so, which has now got to the point where it has started to sound serious.
I think I may have found the cause - five of the hydraulic lifters have a clearance of about 0.8mm from the cam - the spec is 0.4mm max according to my Haynes manual. Could I have some opinions please:
- would wear to this level cause this symptom?
- would it do any harm to leave them for a few more thousand miles?
- when I do get round to it, can you suggest anything else I might check at the same time - ie when I've got the camshaft off.

thanks

 

[turbopete]

hydraulic tappets as a rule can do nothing but rattle when they fail. the excessive clearance is due to them hot holding the oil in as required to keep them full, so i think actual wear will be minimal. to get that level of wear your cam would probably be shot! running it for a while should do no harm. its possible that using an oil flush and a good quality oil change may reduce the rattle, but unlikely. also i have a similar engine in my e300 turbodiesel W210 and the injectors do start to rattle in them too, so its possible that the injectors are the noise not the tappets. the injectors in my case go silent above approx 1200 rpm. tappets will rattle constantly.