Oil perhaps observed from below in defective bulldozer (4)
I believe the answer is:
lube
'oil' is the definition.
(synonyms)
'from below in defective bulldozer' is the wordplay.
'from below' says the letters should be written in reverse (in a down clue, letters go up).
'in' says the answer is hidden in the clue.
'ebul' is hidden in the letters of 'defective bulldozer'.
'ebul' reversed gives 'LUBE'.
'perhaps observed' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for lube that I've seen before include "oil" , "Grease (abbr)" .)