Tomo - IMO you have an impossible task to conclude % or aggragate losses due to engine 'issues' much less outright failure. Lack of eye witnesses in cloud cover for a/c shot down near airfield, 262s shot down in air to air in which pilot was KIA, 262s lost due to engine failuren, non-combat, but records lost or never reported, etc.
I had a real interesting time over 10 years of parsing USAAF 8th AF MACR's to separate into 'air to air', 'unknown but enemys fighters in area' ; Losses due to flak', 'losses unknown but on way home after strafing', 'Pure unknown - such as bad weather present, no fighters seen, 'not at low altitude (icing, oxygen mask failure, unexplained mid air explosion, etc'): 'pure mechanical failure of engine, coolant'; 'structural failure'; Pure Unknown - no survivor/no witness/no enemy contact reported but aircraft and pilot MIA.
Much refinement from MACR achieved in cases where a pilot Questionaire was completed after returning from POW status - and they often contradicted the witness/Macr conclusion.
You have smaller sample but far worse documentation sources confronting your research.