LIFTER ticking

I have read many posts regarding lifter noise. My 95 S420 has intermittent ticking with no particular pattern. I gather clogged oiler tubes are the likely culprits. My questions are :

1. Does one replace them or clean them?

2. At what mileage is is smart to replace timing-chains and tensioners?

3. Can the chains be replaced by attaching to the old chains and winding through?