Replacing the valve stem seals in a 1988 560 SEL.
Back ground
Even though I wear a suit to work now, I have wrenched plenty of engines in the past. I have pretty good mechanical ability in general. However, I am not a professional mechanic that earns ever cent they charge. Quote from local mechanics to replace seals $500 to $600. Cost of parts ordered from the parts shop (seals and valve cover gaskets) < $30.

Tools I used
Air compressor, extended sparks plug air fitting, needle nose pliers with a 90 at the tip, big magnet, and a few basic hand tools. And an overhead cam valve spring compression tool. Not available at the five parts store I tried, ended up buying it at a tool store (KD brand).

The procedure
I am leaving some details out that are common knowledge. Remove spark plug wires and spark plugs, remove valve covers. There are a few hoses and wires in the way, I used bent coat hanger to keep those parts pulled back and out of the way. I pulled the fan at the front of the engine to access the 1-1/16" nut to rotate the engine when needed. Position the cam so that the lobes are not in contact with the rockers on the first cylinder you are working on. Use the spring compressing tool to compress the spring so that the lifter will slide out. It is very important that you do not mix-up the lifters and their location. That is why I did one cylinder at a time. If you put the wrong lifter in, you run the chance of premature wear damage to the cam. After the lifters are out, pull the piece that sits in the top of the valve spring. This is what the lifter rubs on. I then took a piece of straight coat hanger (12") and slid it into the spark plug hole of the cylinder I was working on, rotated the engine until the coat hanger is at maximum distance out of the hole. That would indicate TDC. Compress the spring again so the valve comes in contact with the top the cylinder, this will break the valve loose from the spring and insure the valve wont be dropping into the cylinder if your air supply fails. Next install the air connection to the spark plug hole. There are a lot of different ways to do this, but I used compressed air. It will take about 90psi to keep the vales in place while pulling the clips out. Use the spring compressor tool to push the spring down past the retaining clips. I used a large needle to separate them from the valve. Next grab the pieces with your needle nose pliers. A magnet can be used to accomplish the same thing. It just doesn’t work when reinstalling the clips. One thing I learned half way through was to position a large magnet at the base of the spring to catch the clips in the event you drop one. If you drop one it will add time and cost to this job. Now pull the spring assembly out. The top of the valve stem will be exposed with the old valve stem seal fastened on like a bottle cap. Removing the old seal is tricky because you need to pry it out from two separate sides without damaging the valve seat stem. After it is out clean and scotch bright the valve seat stem. The new valve seals should come with installation tubes to prevent them from snagging on the tip of the valve. Oil the new seals before sliding them in place. It takes a lot of force to snap them in place. Reassemble the valves assemblies in reverse order and move to the next cylinder.

After thoughts, I broke the plastic cam oilers ($10 for two kits). A lot of small tubing and other plastic parts under the hood are very fragile after 10 plus years of heat, so be careful. A dropped valve spring clip can take an hour to locate, start with a couple extras if you are doing the project on the weekend. Carb cleaner is great to clean parts that drop on the ground. This job took me about eight hours with a few minor mishaps and lost parts. I a sure there are more efficient ways to accomplish the same task. I chose one that I felt had a lesser chance of me screwing up my engine. Am I glad I did it? Yes, it saved me $600 bucks and I learned a few more things about my car for the next repair. (excuse my grammar)

The spring tool I used was a KD 3087 at a cost under $50. You can see the tool at most online tool stores. It gave me some problems that duct tape solved.