Regarding the cleaning of the used injectors...inquire the cost and what they do. Here, U.S., the cost for servicing a set of four is about the cost of one new injector. The service includes the ultra-sonic cleaning and pressure testing. You will want them tested with more than 10 bar of pressure over its fuel pressure release/regulator valve(FPRV) limit on the rail. Or ask them what they do regarding testing pressure...they should know what the limit is for the FPRV you have. My FPRV has a 145 bar limit. So, you need to confirm the pressure they test them at, also, if they compare spray pattern so to know the nozzles are spraying equally. I have a set of four I just removed that have 97k miles on them. They were fouled somehow and my long-term mileage average has now gone up from 23 mpg to over 28 mpg. I am still not sure if it is worth the cost to have the removed injectors checked...and I may just toss them out. Still undecided.