I assume my pump is dead since there is no liquid comes out and tank is full. My little research showed that this is quite common problem.
I found bunch of different pumps on eBay. Starting at $7 for aftermarket and ending $40 for OEM.
Can anyone advise on that one? Does it make sense to by OEM with tends to fail? Any suggestion on aftermarket one?

Any input would be highly appreciated.

I just got a cheap £10 one from eBay, been fine for 6 months, spray just as powerful.

Why did you go cheap route?

I've had used similar after markets for the other cars we have had and they've been fine. But ultimately, I was 17 at the time, and needed to try and save the money, so I decided to take the risk and go the cheap route on this particular part. It's a fairly basic part with no real load on it

Maybe I should give a try. OEM failed anyway

Make sure u press the button all the way. When I first got my car, I thought my pump was broke. It was full of fluid like yours. I finally figured out that you need to press all the way in. If you press it partially, it will make a sound but no water. Try pressing all the way.

Thank you for tip. I will give it a one more try today.

No, it doesn't work.

My water pump malfunctioned back in Oct-2011. I had no choice but to have it serviced in the dealership.

The cost of the water pump was $327CAN, thermostat was $45 and labour was 2.1 hours. With the other misc charges and tax, the total invoice was $715CAN. I did get 15% discount on parts.

For engine parts, I insist on OE part (MB parts, not even OEM). I am not a DIY person so I cannot afford to pay for the labour again.

OEM - Original Equipment Manufacturer. In this case MB. Same thing.

Problem is from what I can see, the definition of OEM in some online stores are misleading. For example, Mann supplies air filters to MB but if they sell Mann brake pads (they don't but just as an example), they are still considered OEM.

I do find the original suppliers of some MB parts (Mann is one example) here but not for every parts.

In this case scenario MB puts their label on it. But I don't know to much of it. I bought genuine filters from MB and there were no word from Mann. Maybe it is second choice. But OEM was always standing for original parts next to genuine. OE is aftermarket.
Everything from my experience and observation of others.

i learnt from this forum thatm Mann are the supplier of MB air filters and oil filters. i have been using them for a few years with no issues, just make sure the oil filter is made of fleece. Mann filters are probably the only non-MB engine parts I use.

Check this out:
http://www.autohausaz.com/pn/1120940604
http://www.autohausaz.com/pn/HU7185X

Last year I bought engine filters with MB stuff on it in MB package. I saw Mann filters and passed them.

"Genuine" parts will be be labeled "Mercedes-Benz" and will have the three-pointed-star logo. MBZ subcontracts the manufacturing for many of its parts. Those subcontractors are allowed to resell those parts themselves, but they are NOT allowed to mark them as "Mercedes-Benz" or use the star logo. Examples include Mann, who makes the oil and air filters for MBZ, but also sells them under their own OEM label. Lemfoerder makes the front control arms for the suspension for MBZ, but also sells them under their own OEM label. Now, would I buy Mann control arms or Lemfoerder filters? Probably not. Each of these companies has a specialty. I would buy what the specialize in making.

I got your point. So I guess I wrong. But I still consider OEM to be MB.

Oh, I do, too! It's just that they can't put The Star on the parts. And BTW, this is not just an MBZ thing - this is the case all over the world with most every major manufacturer. An not just automobiles.

Exactly my point. Once a manufacturer supplies even one part to MB, the online store would identify this manufacturer as OEM no matter which parts they are selling.

If you know the supplier of a given part, to buy OEM parts are certainly OK. In this case, I would not be concerned to buy Lemfoerder control arms anytime.

Well, now I now.
Btw, I ordered continental VDO pump. $22 shipped. Figured it is worth a try. Had good reviews and made in Europe.

Stick OEM, anything else will be cheaper but it's a false economy. OEM parts longevity is always better.

OEM failed me. VDO is very big name. As long as it is not made in China I will be fine.

at around 40 bucks i would go Mercedes. My CLK550 is in the shop for a few things including this.
Motor trans mounts, outter tie rods, keyless (driver side) .

I would DIY most of it but since i have an aftermarket warranty ima let them deal with this.

A shame since i only have 30 or 31k miles on mine. Its typical for these mounts to last 20-30k miles... MY clk350 had them changed at 27k miles.

Still love the car and cant see myself parting with it any time soon.

I believe that continental vdo is their supplier. Mann situation.

OEM failed you? So what after 10 years? Everything breaks eventually.
If you buy another OEM, you can assume it'll last another 10 years. Is that worth $40?
Who knows how long the cheaper pumps last...

That is a true as well. But still not long enough to fail. This is not everyday use pump.