There are three or four each side. Rather than a drilled hole, they are a semicircular-shaped pressing on the inner side of the welded lower sill flange to form gaps into the bottom of the sill cavity.

Easiest to see with a strong light and mirror unless you can safely raise the car to get underneath. They can get blocked with road dirt.

You will need a short length of stiff wire (try a straightened paperclip). If one or more holes are blocked then water can collect in the sill and eventually find its way into the car, especially if there's some corrosion in the sills.

Clear out the holes - if you get water coming out then they have been blocked.

The wiring loom to the rear is hidden behind a kind of hard insulation which is glued to the inner face of the sill. There are plenty of apertures for water to get out from behind this, e.g. where the wiring loom emerges.

At the front of the sill - in the front wheelarch - there is a solid rubber grommet that seals the front end of the sill cavity. I guess the hole it seals is there to allow the sill to be wax injected after assembly and painting of the body shell. There's also a similar sized hole in the bottom of the wing to let water out. This is all hidden by the plastic blanking plate behind the wheel which is only partly successful in keeping water and crud out of the void behind it(especially if the rubber seal is poor). The blanking plate is held in with 3 self tapping bolts, can't now remember if they are 8 or 10mm without looking! If you need to get it out, turn the steering onto full lock to improve access (or jack the car up and remove the wheel if you're not as lazy as I am).

On my old M535 some idiot had replaced the grommet in the wrong hole after repairs. The crud built up in the void and eventually reached the level of the hole in the end of the sill. Water then poured into the open sill. The drain holes referred to above were blocked and hey, presto! I had a major leak.

As well as having wet carpets, the car would sometimes leave an obvious trail of water after being left out in the rain, parked on a slight slope outside my house. This was because the water collected at the rear end of the sill and then poured out of the front when the car was driven onto level ground.

A note of caution: once I had sorted this out on my car, being a fairly conscientious sort of bloke I then sprayed anti-corrosion wax into the sills. Even though I cleared out the drains afterwards, the wax eventually "flowed" in hot weather to block the drain holes again, so I got wet carpets again...the moral is, clear the holes regularly!

Finally, the thick under-carpet insulation is *very* difficult to dry out - it can hold a lot of water. On mine I resorted to lifting the carpet as far as possible and very carefully cutting the insulation with a knife where it rises up over the transmission tunnel. I could then remove the wet sections from the car to dry them out without having to strip out the whole interior - the car was my wife's daily driver!
I used a rolling pin (as in pastry!) to squeeze the worst out, then putting the sections in the domestic boiler cupboard, standing them on edge to help the water drain. Don't leave it in the car - it will rot the floor quickly as well as making the car smell bad inside.

Best of luck!

Steve Offley - '87 M5 Euro

I discovered some wetness under the carpet on the floor of the rear passenger area. I cannot figure out where the water is coming from. Here are the facts:

1) I had just finished washing the car, but did not see any sign that water had entered through the door seal.

2) The car had been driven in the rain recently, but I didn't see any signs that water was entering through the floor board.

3) The floor of the front passenger side is dry.

4) The water appeared to have been there for a while. There is a piece of padded rubber under there that had disintegrated to an extent. The same piece on the driver's side is fine.

I have only had the car for about 3 weeks. I will be checking with the previous owner to see if he was aware of any leak back there. However, he cared for the car meticulously and I'm sure would have taken care of this problem if he knew it existed.

Are there any known areas where water can enter back there?

Thanks.

Sean
'88 M5
'76 2002