FRying: as a member of th eflight deck community, you would not be expected to have access to maint manuals. The engineers when they sign off your entry as checked and found to be within mm limits should alwayd actually give the mm reference, not just a bland statement. For 737-300 they are:
71-00-00 p241 - 242
I. Oil Consumption Limits
S 842-053-C00
(1) Normal oil consumption is less than
0.4 U.S. quarts/hour or
0.1 U.S. gallons/hour (0.38 liters/hour).
S 842-054-C00
(2) If you find increased oil consumption that meets the conditions that follow, you must find the cause and take corrective action; do the engine oil trouble shooting procedure (AMM 71-00-44/101):
(a) Oil consumption that shows a gradually increasing trend.
(b) Oil consumption that shows a sudden step increase.
(c) Oil consumption that is more than
0.8 U.S. quarts/hour or
0.2 U.S. gallons/hour (0.76 liters/hour).
S 842-055-C00
(3) Oil consumption must not be more than a maximum of
1.6 U.S. quarts/hour or
0.4 U.S. gallons/hour (1.5 liters/hour).
So it seems that your hypothetical 737-500 is probably within the MM71-00-00 p241-242 limit.
There is however something that does cloud the issue. The above figures are for CONSUMPTION, ie the engine is 'burning' or 'drinking' the oil. The puddle on the floor and wet cowlings suggest you have a leak. Leakage limits are given in MM 71-71-00 p601 onward, but these refer to leak rates from individual drains and it seems the engineers in your case cannot find anything coming from drains?
Anyawy, moral of the story is if the engineer has quoted chapter and verse with regard to mm refs, be happy to believe him. If he jut says 'within mm limits' ask to see the limit as he surely has checked it and will have it to hand?