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Those tubes are used on the early Great Wall utes, which had Toyota motors. They are much cheaper than from Toyota if you can find them at a Great Wall dealer. The starting point for the idle mixture screw is turn it right in until it gently seats, then turn it out one and a half turns. A motor with nothing wrong should be within a 1/4 turn of that. With a warm motor at idle you should be able to turn the screw in and out by 1/4turns and pick the smoothest, fastest idle with the screw furthest in.

Hi Ben, Welcome aboard ! What you describe is not unusual, & probably been experienced my mamy on here, with older K Series engine. There are two quite distinctly different issues here. The aluminiun spark plug tubes, are soft, as they are aluminium. They play two important fuctions. 1. The flat section of the bottom on the tube, through which the threaded section of the spark plug protudes, is "clamped", between spark plug & head, when you tighten the spark plugs up. Over time, this area of the tube gets thinner, & sometuimes even cracked & worn; as a result of the spark plug "tightening down action"; is not perfect, & in worse case can suck oil into the cylinder. 2. The second function is to prevent oil return path, from rocker oil feed, to sump, from leaking. It has a rubber under the top lip, to seal at that end, & the spark plug tightening on the flat at the bottom, to prevent from the bottom end. Because tha aluniniun is soft, the tube can effectively "elongate", & it will not seal properly on the rubber seal at the top. Solution, new aluminium tubes & rubbers. Bear in mind, that in your first picture, that whole void in there is wet with hot oil return to the sump, whilst the engine is running. Also check the sump breather relief valve on the top of the rocker cover. If that is blocked it will exaserbate oil leaks inside the sump/block/head area. That valve feeds back into the inlet side of the head, so you can easily understand the implications, if that is stuck "open". The "wet" spark plugs would maybe indicate a mixture too rich, rather than too lean, & maybe an issue with the needle & seat & float in the carby, not cutting off fuel flow properly. Maybe time to remove the carby, & completely clean & reassemble. Don't forget the crankcase pressure valve that protudes from the top of the rocker cover. Often neglected, which results in them being fully open, or fully closed. Take your time, & work through these three (3) areas, & I'm pretty sure, you will resolve your current issues. Cheers Banjo