The reason you may have a leaky oil pan is simple. your car is 32 years old and it has a few dings in the pan. Which warps is, so there is no longer a tight seal. Secondly, the gasket is 32 years old. But if your reading this you already know these things, and just need a few tips to get the job done.
One of the side effects is improved performance dont you know.I gained a noticeable amount of extratra "pep" or a "few more scolded cats under the hood" after replacing the pan....
Do not under estimate how dirty this job is or how long it will take. Start it in the morning just in case something goes horribly wrong. like you accidentally fold the gasket or something. Some sites on the web say it takes no more than one hour, but thats if your have done it before. It is a simple job, but as you will see, sometimes the car will through a monkey into the blender. If you know what I mean....
Step 1: Tools
5mm Hex socket,
6mm Hex socket,
Torch wrench (I got mine on the day from Kragens for $9.99, works good)
A 3/8 to 1/4 converter to go from the torch wrench to you Hex, (if you need one)
Jack stands or a pile of 4x12s ( I used 4x12 railway sleepers until my neighbour saw me and was so shocked that he lent me his stands).
Oil catcher thing -- 4 litres plus ,
Disposable gloves -- Not a requirement, but useful.
Old cardboard boxes (to lay on)
All Mercedes are in metric! Using imperial sockets or wrenches may work (sort of) but you'll just round the nuts off. And no one... NO ONE wants round nuts.
These will do and they are cheap. http://www.amazon.com/Neiko-7-Piece-8-Inch-Socket-Metric/dp/B000IQNMQU/ref=pd_bxgy_hi_img_c
Step 2: Parts
Oil pan gasket
Step 3: Remove Oil Filter
This is done so all the oil will drain out quickly
If your car is anything like mine or just about any older mercs, the vacuum lines are old, brittle and the rubber connectors hard and fragile. So it is a good idea to note the configuration or take a pic of them. But be sure to hold them out of the way as you remove the filter. One time at band camp, I knocked the vacuum lines off at the very spot you'll be working in. The car started alright, but I couldn't turn it off again with the key. It took us for ages to figure out the proper combination. It was like trying to crack a wall safe while suspended from the celing...or something.
Step 4: Time To Play Car Jenga
Use the 13mm socket or a wrench to remover the oil pan plug. Oh and put the thing you plan to catch the oil in under the plug hole.
Let the oil drain as long as posible. You can put the plug back in to stop it dripping on your head.
Step 5: Removal
Starting at the drain hole start unscrewing the hex nut in clockwise direction. It is a good idea to keep them in the order for the replacement since some are longer than others.
Step 6: Clean and Replace
Position the gasket on the new pan and hold in place with a hex nut.
Finger tighten the hex nut to hold the pan in place
Lightly tighten/finger tighten the hex nuts ensuring that you replace the nuts in the same order they were removed.
Lightly tighten the nuts with the ratchet and 5mm hex socket IN A STAR PATTERN.
***WARNING WILL ROBERTSON, WARNING***
If you dont tighten in a star patten you WILL warp the pan and you will be in the same position you were in at the start. leaking oil.... and $36.94
Tighten to 11nm or 10 fp (foot pounds) with the torch wrench. Put in the drain plug while you are here.
Drop the car and replace the oil.
Because you have drained all the oil out of the oil lines as well as the pan, it will take more oil than you might supect to get it back to proper levels. Pour one of your oil packs in and wait for it to settle.
Start the car for 10-15 secs. Check the dip stick and if it's low stop the car and add oil.
Check for leaks and good oil pressure. and off you go, slightly greener than before.