Cars here repaired in systematic investigation (8)
I believe the answer is:
research
'systematic investigation' is the definition.
(I've seen this before)
'cars here repaired' is the wordplay.
'repaired' indicates anagramming the letters.
'cars'+'here'='carshere'
'carshere' with letters rearranged gives 'RESEARCH'.
'in' acts as a link.
(Other definitions for research that I've seen before include "Examination" , "Investigate through study" , "Look into" , "Scientific investigation" , "Experimentation" .)