The oil will burn off any manifold in minutes, not hours.
you need a bright light and look carefully running (idling).
look for leaks.
or it can be something, else.
guessing 93 vitara Europe etc. is 93 Sidekick USA.
the Valve cover and the Dizzy are infamous leaks.
the dizzy will leak at the 2 o-rings , at the base to head juncture is common as nails.
it hardens and cracks.
do not pull it unless you know how to Re-TIME IT. ! my timing pages shows that.
How to set ignition timing
mine leaked down back of block, to the left (drivers perspective) and then dropped to the Exhaust headers collecter point, constant smoke.
$1 fix, 1 hour labor.
but being clean first like top post then looking after a hot run , will show you where the leak is , every time.
cheers