the main problem with these pumps (part number 815049) are: 1. Expensive: about 400€ for a new one, very hard to find a working old one. 2. Membranes: the membranes used in these pumps get broken quite fast and there is limited supply of new ones, making repairs expensive or unreliable. 3. Seal: the seal is sometimes leaking petrol into the oil.
Main symptoms of failure are: 1. LIMP mode after reaching ~3500 RPMs (about 120 km/h (75 mph) on 5th gear), nearly complete loss of power which is dangerous on highway. 2. Misfires while accelerating. 3. Error P1191-52 Fuel Pressure System Malfunction.
I know that there were Siemens made pumps which had an extremely short service life. Continental made pumps replaced them but the stated problems persist.
I also read somewhere that ethanol in petrol dissolves those membranes and it is hard to evade this since all 95 octane petrol sold here (I live in Lithuania and I believe situation in other EU countries is the same) contains at least 5% of ethanol in it. Maybe 98 octane petrol is a solution.
After searching for a while, I've found no stable alternatives for this pump. Some people use 8200199822 pump made by Rexroth. It uses valves, not those nasty membranes and price is considerably lower (less than 150€). All you need is an adapter (mounting kit) which was in market for some time and I am unable to find it on sale right now. But I cannot find any feedback on this.
Also, there is a guy in Belarus who offers a similar fix but I am a bit cautious of sending such amount of money with no guarantees (and a considerable customs charge, I suppose). Maybe someone has tried it, please do give opinions. Here is a post made by a Russian guy who used this service and is happy with it. Text is automatically translated from Russian, can't vouch if it is translated correctly for I do not speak Russian. https://www.drive2.com/l/8666498/
Maybe anybody has heard of other solution to this problem. Thank You very much!
