Mercedes A170 L 95km 2002 - Constantly burning out washer under the injector.

I warmly welcome.
I am asking you about the problem of the injectors in the above-mentioned car, ie Merc versus 1.7 CDI 95 HP class, 2002. Long version.
Currently, the car is at the mechanic's, but I have a suspicion that it pounds me quite a bit in the bottle, so I would like to learn a bit here. The car after the regeneration of all 4 injectors over a year ago (a set of one injector - I do not know what it means, but it cost PLN 500 + adjustment, cleaning and sealing, the other 3 also adjustment, cleaning and sealing + 1 sprayer). Since then, on average, every 3-4 months it burns out the gasket under the injector. The last failure happened a week ago, today I visited a mechanic, he said that you need to "grind the injector in the place where it touches the washer because there are crooked / uneven surfaces, therefore it burns the washer under it" additionally said that such a procedure must be done on all injections . (in the picture I marked what's going on, only there is probably the washer still there) after a short conversation with the mechanic, he explained to me that the injectors were regenerated only inside, outside no?! ??! in addition, one injector flew out of his hand onto the floor. And my questions now: Can it be sanded down, does it help at all? Will the stroke between the piston decrease? The sprayer is probably what they want to grind down ... Or maybe they mixed something up during multiple disassembly and assembly? could the fall of this injection cause any additional damage? As I wrote earlier, I suspect that they themselves do not know what they are doing and I am paying for it.

hello, look at the seat surfaces, washers and the injection socket in the cylinder head

Milling slots. The injector after the fall to be re-verified on the table. I have not seen an injection so damaged that it would burn out the washer. I saw the head often. And mechanics sometimes forget what to do with even used washers to seal.

pay attention to the socket in the head maybe there is a reason

Okay, after work tomorrow, I'll be there again. I will add that before the repair of the injectors, the washers did not burn out and when I bought the car, it ran without any problems for a year and a half, but there was a big problem with starting in winter + high fuel consumption and thus a lot of smoke. After the injectors were repaired, they started ie miracles with the washers. Is there such a probability that they did something with the sockets? The injections apparently came out relatively well, they gave up quickly. I called a real service, it seems to me and they said that every time I give Sue new washers and nuts? I don't see the position of the nut on my repair invoices ...

In my opinion, there are three possibilities:
1. Gnbiazo in the head does not fit perfectly. I saw deep scratches from cleaning with a screwdriver, dented dirt, burn marks. There are cutters for cleaning and checking the socket. Look for an "injector socket cleaning cutter" and maybe ask a mechanic if he cleaned the socket.
2. The old shim was reused. In many brands it succeeds, but in others it burns out the pad fairly quickly
3. The old washer has not been removed and there are two. I've had such a case recently. Must be checked prior to replacement.

I always mill the nests, if it wasn't blowing only licks, so that there would be a flash. Sometimes I will align the injector with the same cutter, but without the mandrel. I always give the washers new, the cost is PLN 5-6 per piece. Recently, I bought the most expensive for 1.7cdti an unusual shape, only on the website, PLN 22 / piece.
That mechanic of yours is some beetroot, go somewhere else.

After 1, the injector seats must be milled! but delicately, so as not to collect too much, as a colleague wrote above, it has to be clean and "shine". Nominal shim 1.5 mm, after multiple milling 2 mm.
Secondly, the element you have marked on which the washer rests is called the injector bumper, if it is distorted, damaged or after a fall. Any attempt to fix it will not help! Any turning, grinding, milling, even if I don't know how I did it, it will blow anyway. If the bumpers are deformed, unfortunately you have to buy new ones. Believe me, I used to fight 2 slightly damaged bumpers, they had one deep scratch in the place of the washer. And believe me, after a day of figuring out, grinding, turning a button, it came out. The reconditioning guy sold me 2 new bumpers after fitting the problem was gone forever, and warned me that these are irreparable things. Too high accuracy and precision.