My 1997 E300D NA has lifter tick.
 

It's very slight right now, how hard is it to change it out compared to the OM603? It will be 4 lifters per cylinder right? 2 intake and 2 exhaust?

It might be dirty, have you tried adding any oil cleaner to the oil to clean it out? I suggest a Rislone treatment before tearing into it.

Depending on the cost of lifters. I test lifters in my drill press. Just put them in a tray of fluid and see if they pump up and pretty much hold. Each one on removal should have a location mark put on it.

Why especially on your engine? There has been mention of the oil feed passage to the lifters being blocked. Partially obstructed is a better guess. After a test taking them apart cleaning and retesting them. You can buy one new lifter for comparison purposes. The ones that test as new if any after. Your call then.

Again what to do can depends on cost and circumstances. For example If I found after proper internal cleaning they were testing as good as new. I might reuse them if really expensive otherwise. Now if they all test good right out of the engine. You might think their oil feed is involved. The day where I got a set of new lifters for 15.00 for a chev engine is long gone.

As mentioned first starting with some type of cleaner. A bottle of miracle mystery oil in the base oil could be additional to whatever else you try. They make a big deal out of its ability to quiet lifters sometimes. Nothing is going to quiet a worn lifter though. Built up varnish and buildup on the valve port inside the lifter being cleaned I can see. If the car has been on a diet of synthetic oil it has some cleaning ability itself compared to dino oil.

Or if you decide to buy a new set before starting. Rather than just throw the old lifters. Try testing them for experience at least.

Just run some transmission fluid in the oil for 20 miles and change it. Just as easy to change oil in as a 603.

No I haven't tried any additives yet, I'll give those a shot and see what happens.

Teaspoon full of trans fluid is enough to clean the lifters out. I’ve done it a few times and have success. It literally doesn’t hurt anything. Cheaper and stronger than half the junk oil cleaners you’ll buy in the store. Probably missed a couple oil changes here and there and next thing you know clogged lifter. Depends on mileage too...

They could just be worn out. Good news is they’re extremely cheap if need be.

Don't agree with "extremely cheap" but those little hydraulic lifters can be a PITA!
I couldn't get a lifter to quieten down with an additive or running synthetic oil for a few tho miles and I didn't try the trans fluid idea but I ended up replacing all of them and they weren't exactly "extremely cheap" if you consider they cost me something like $15 - $20 each, I don't remember exactly.
And the 606 needs 24 of them!
Also went thru that on my OM603 and put a smile on my face afterwards. The engine might not have been in danger of wearing or failing prematurely because of a sticking "cam follower" but it is plain embarrassing to sart up a fine car and hear a tick tick tick! :o
BTW I didn't want to risk aftermarket quality so I ordered them from a dealer. whatever - my engines all run nice and quiet now!
DDH