Oil Leak

I think you're looking in the wrong location for your leak. If the oil is splattered all over the engine and on the hood, that indicates it's coming from the engine under pressure. Otherwise, it would hit the ground or accumulate strictly on the engine surface. That isn't what you're describing. You more than likely have an oil cap or dipstick that is not sealing properly. The last choices would be the oil pressure sending unit or last choice of the valve cover gasket. Remember, the leak is activated by oil pressure! Go to a car wash and thoroughly clean and degrease the engine and engine compartment. You can't isolate it if it's concealed by previous residue. SIMPLE GREEN works well and is BIODEGRADABLE. Drive the car for at least 10 miles; AND, get it up to freeway speed for a short distance. Then locate the leak.

probably the valve cover gasket by the sounds of it

Unlikely...his symptom is a high pressure spray of oil. It would more than likely be forced DOWN were it coming from the valve cover and not on the underside of the hood.

I took it to the same mechanic twice and showed to them that after they replaced the oil pan the the host, the oil still splash up i've wasted 400 already to replace those two, they seem to can't figure it out the source of the leak it was a while ago, somehow the leak stopped, but now it's going on again (maybe because of the weather, cold?)

DUDE!...locate the leak yourself! It isn't rocket science. The oil will spray out the engine more readily as the level is near full. As the oil level drops from leakage, it will spray less. Cold weather will only effect the viscosity, (resistance to flow/thickness) of the oil when it's cold. When it warms up, it really is no factor. Like I said before, it's a pressure related leak. Check the filler cap, the dip stick or MORE THAN LIKELY, the pressure switch/sending unit. About your mechanic, GET A NEW ONE! Locating a leak is not a great task. They are taking advantage of you. RULE OF THUMB; always have a general idea WHAT the problem is BEFORE you try to get it fixed. Otherwise, you'll pay for unnecessary repairs. In your case, since they failed to correct the problem, I'd seek an adjustment or refund on the labor. AND, that is a reasonable request.

1992 acura integra 1.8 made in japan models. the top air breather filter housing, there 4 phillip head screws(10mm hex) cover about 3 x 4 inches under this cover is the crankcase ventilation filter element . check if dirty,replace(rockauto.com about $12.) check pvc valve. this stopped my oil on hood & pass emissions