It is a split keeper (2 halves) sitting on the retainer ring - you can see it in the picture around the stem. Use a magnet to pull the keepers once the spring is compressed.

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Prost!

Make sure you have cylinder on TDC and the valves held closed by compressed air. After compressing the spring, give the compressor a tap or two on top with a hammer to loosen the split collets or keepers that are positioned around the top of the valve stem. Block any oil drain holes in the head with paper towels etc as the keepers can get away. I keep a pencil magnet handy to retrieve them.
After you change the stem seal, place the spring and compressor back over the valve and push down on it as you replace the keepers. I use long tweezers and thick grease to hold the keepers. Once you are sure the keepers are correctly in place release the compressor and diesconnect the air line. I give the top of the valve a sharp rap with a hammer and punch to seat the keepers.

Okay, I was able to see the split retainer. I compressed the spring and hit to top of the tool to loosen the retainer but it won't budge. As I move up and down with the tool the valve goes down with it if I don't prop the bottom of the valve with a wooden block. I am right now testing this procedure on an extra head I have, so I have access to the valves on the other side.
I will use compressed air on the real job tomorrow; today is practice so I don't mess things up since this is the first time I am doing this.
I will try again after lunch...

I got it!
I just had to tap with a little attitude
The dis-assembly and assembly went great I now know that I can do it on the car.
My next question is the hydraulic lifters. I tried to take them out to see how they are in place (I have some new ones in a box) but they stayed in place with just a little play up and down. I turned them with my finger, I even held the back in place just in case this is screwed in but no progress. Do I need to punch them out? I would hope that's not the case
Anyway, is it a good idea to replace them as a preventive?

Oh, before I forget, how much play should there be between the stem and the guide? How does one figure out that it's ok?

The play will be minimal and inconclusive when you have compressed air in the cylinder as the valve will be supported by the seat. If you feel brave you can release the air from the cylinder and wiggle the valve stem, but never let go of it as it may drop out of reach into the engine. As to the spec for the guide play someone else will need to give you that or search out a repair manual.

Remember that just doing the stem seals could be a band aid for leaking guides too. This was the case with my 300TE until I rebuilt the head.

This was the tool I used

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

That's interesting, I thought replacing the stem guides was the realm of the non-mortals...
What's the name of that tool? Where did you get it? How easy is it to use and how does one figure out how far to seat the guide?

The shop I queried about replacing the guides claimed that the head had to be removed....is this the case? I suppose once the head is removed doing those tasks is not that big of a deal as long as one has the correct tools...

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I intend not to remove the head for now even though I have an extra head that I can send to the shop ahead of time. If it's only the seal then I will be happy to postpone a major repair for another time after I go back and control my priority list of things to do in life. The 190E has taken up a lot of my time fiddling with the CIS to no avail yet the problem was much simpler (I think).
Now, how about them tappets/hydraulic lifts?

Sorry for the confusion, that is for the valve stem seals. As far as I know, the head must be removed for the guides. I removed my head and sent it off to the shop for him to clean, skim and rebuild. You can do it yourself, but for what its worth as it has to be sent off to be skimmed anyway, might as well just let the pro do it.

You should not have any consumption problems for the time being, but in the near future, you may start losing a quart every few thousand, by which time you gotta realize the guides are bad, not the stems....and all that burned oil is reducing the life of your cats.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Any idea why your guides were already worn with only 90k ish on the engine? How much did your mechanic charge to rebuild the head? (I may go that route someday on my 300E)

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

^^
Good question because my 190E has 100K miles.

My 300E is at 140k.....I've read that the guides last about 200k.....currently its taking about a quart of oil every 1000ish miles depending how its driven. I'll try just getting the seals done first though, hopefully it fixes the issue for a while....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Changing guides requires removing the head. It also requires regrinding the valve seats to make them concentric with the new guide. And since the seats are re-ground the valves need to be re-faced also.