For oil changes, if you don't wish to crawl underneath the car, you'll need a 'Topsider'. I personally use a 'Liquivac' with great results. Do a search here on how to use it, and on Google for online vendors.
To access the oil filter you'll need to remove the air filter assy -- 10mm socket (3 bolts hold it on) is what you'll need. I personally hand tighten the oil filter on and off with no problems. Remove three 10mm bolts on top for air filter change.
For tuneups (spark plugs) I use some good needlenose pliers to remove the wires -- grab metal jut on side of wire and pull out. DO NOT
try to remove wires from outside the metal area or you'll likely break the ceramic material inside the wire. ************************ also sells a wire puller if you want to spend the $$. For plugs themselves, a regular 5/8's spark socket with extension will do.
To change the distributor cap and rotor (on 300E), you'll need to remove the fan shroud and distributor cover. (some state they need to remove the fan blades or fan clutch assy to remove and replace shroud ... I've never had problems removing shroud with fan in place) (no special tools needed). Three 5 mm allen bolts hold on cap. A long allen wrench will be needed to access and remove the bottom bolt. Three 2 or 2.5mm bolts (forget which) hold on the rotor. Don't tighten these too tight, or you may have strip problems later due to their small size. Locking washers hold them on well.
Fuel filter change requires a 17mm box wrench and a crescent wrench -- or two 17mm wrenches. Five or so 10mm plastic bolts hold on the protective cover ... one requires a long extension to remove.
If you want to venture into serpentine belt replacement, you'll need to remove the fan clutch or just fan blades. Depending on MY of your 300E, fan blades are attached by 3 allen bolts each, 4mm I think. To remove fan clutch, you'll need a special 5mm allen socket tool (so you don't have to remove radiator for space) and a counterholder that holds clutch in place from behind, both available from performanceproduts.com for about $20. Some DIY'ers prefer to use homemade tools (thick coathanger etc. for counterholder) but IMO, save yourself the headaches and buy the proper tools.
You'll also need to slacken belt via tensioner... for this you'll need a 13mm regular socket and a deep 19mm socket.
For coolant flushes, the only tool you'll need is a 19mm deep socket and an extension to remove block drain. Screwdriver to loosen plastic radiator drain at bottom. Oh, and a 14 mm socket to remove bleed screw on head, if your 300E MY has it.
Basically here is what I'd purchase:
- set of metric allen sockets -- 2mm up to about 7. Autozone sells
a good set for about $10.
- set of metric box wrenchs, both short and long from 8mm up to
- basic set of metric sockets with various length extentions, 3/8's drive.... from 8mm up to about 14mm; deep 17mm to 21mm for move involved stuff.
- socket extensions
- jack stands for under body or suspension work
- ramps are helpful for underbody work as well
You'll encounter the 10mm bolt most often it seems whether doing engine or body work on the 124.... followed by the 13 and 8.
DIY'ing is both fun and rewarding so I'd encourage you to "dive" in and have fun! Don't be intimidated!