I had the same problem 5 years ago, the best method that worked for me is to use a steam cleaner & spray that one the jets so the steam cleans out all the grease from years of usage! for around 20-30mins, then leave it to dry with the doors open for around 2 hours & try to light the oven using the knobs only, it should tick for ignition a few times, then the pilot light should light up & then the jets! use oven knob setting 5 to begin with to get the oven lit, this is the only work around that works...
Richie
December 2020