Engine misfire.

[Mjsykes]

need some help/ guidance. Had a code 72 on the diagnostic replaced both exhaust sensors and still had same read out so left solenoids. removed the solenoids on bank 2 side. cleaned the board checked all solder joints visually and battery checked all terminals and leads. all fine. cleaned out each individual solenoid for debris and replaced all the O rings on the solenoids. Placed back in the car with paper gasket and started the car. cleared the ecu warning light and but had a slight rough idle. the car warmed up and settled so took it for a drive. all was fine. the following day i started the car up the idle was really lumpy. ecu light came up again this time i had cylinder misfire on numbers 5 6 and 7. any ideas?