Times Jumbo Cryptic 1171

[borgeile]

Down to the last four and stumped.
40a Investigators have stamped around, that's agreed - think it's either COINCIDER/S
50a Drug required: he had run into back of apple tree - think it's ephedrine?
44a If not blocked by piano, pass by (6) ?L?P??
41d Stop deal in restricting limits on Omani fuel (6, 3) ?????? O?L

Many thanks in advance - brain broken!

[Lie-in King]

40a Coincided - 'coined' (stamped, around) 'CID'
50a Yes, 'Ephedrine' - 'he'd r(un)' (in) '(appl)e' (back) + 'pine'
44a Elapse - 'else' (if not, blocked by) 'a p(iano)'
41d Diesel oil - 'die' (stop) + 'O(man)i' (limits, in) 'sell' (deal in)

[borgeile]

Thank you Lie-In King! I'm now good and clear for tomorrow's fun.

[Lie-in King]

Happy to help :-)