To get the subject jogging along:
In cruise 600 miles after take off noticed the oil contents gauge needle showed one gallon. Needle slowly reducing towards zero contents. As destination also 600 miles ahead over water, decided to return to base.
Visual observation of No 2 engine revealed trickle of oil. Closed down the engine and with fuel not a problem left max cruise power on remaining engine and descended at 250 knots until stabilised around 13,000 ft. Cause was incorrectly fitted O Ring to oil filler cap. Loss of oil contents confirmed and seems that this sort of problem occurs shortly after take off but for some reason we (I) never noticed until in the cruise.
Saw same type of problem while dead heading in a 737 and invited to jump seat when I spotted the low oil contents and the crew hadn't. In this case incorrectly fitted oil cap.
While positioning downwind for visual circuit noticed the park brake light on. Gear was up. Although the park brake light was not part of the "Lights Test" system (it is press to test), F/O suggested we try the Lights Test switch. We flicked the switch to test and back to bright and lo and behold the Park Brake light extinguished. Unable to explain that one.
Took over from crew who flew the aircraft Manila to Guam. They originated at HKG where scheduled servicing had taken place. On the walk around I checked the brakes for heat. Three brakes only warm (Guam has a long runway so didn't expect hot brakes) but the 4th brake cold. Disregarded this as a bit unusual but no suspicion of anything really wrong. Two hours later landed at short runway in Micronesia (Ponape). Used relatively minor braking but lots of reverse. During walk around prior to departure (45 minutes turn around) checked brakes and same result. Three warm brakes and one cold.
Another two hour leg and landed on Nauru (5600 ft long) and used moderate braking and full reverse as normal. Three brakes definately warm now and one stone cold. Maintenance discovered the cold brake hydraulic lines had been blocked off during servicing at HKG and not reconnected.