sounds like driveshaft, ever check?

It's like 5mm  higher than last time reading, 2 days ago.
I suspected petrol mix into it. No solid evidence yet. but I checked just now in afternoon, it backs to normal.

checked through net, found this :
""""-In certain cases, the oil level may have risen since the last time you checked. This could be due to condensed water (from combustion), condensed fuel or a coolant leak - all are causes for concern.
-Fuel-diluted motor oil (from blow-by or leakage) can substantially reduce oil viscosity and thin additive concentration. The odor of diesel fuel can often be detected right from the dipstick.
-Free and emulsified water is harmful to the oil and the engine. For short-trip drivers, water condensation may be more acute if your engine has the flexible fuel vehicle (FFV) option and you are burning an alcohol-gasoline fuel blend. It is important to remember that combustion produces water in your engine - more water than the fuel consumed. Most of the water goes out the tailpipe, but if the engine is cool, much of it may condense in the crankcase.
-A simple way to detect water in used motor oil is to put a drop of oil from the dipstick on a hot exhaust manifold. If it crackles (sounds like bacon frying) this is an indication of water contamination. Beware that there is some risk that the drop of oil may catch fire.
-Brand new automobiles imported from Japan may have a high oil level due to short-run engine starts (as many as 50) required when the vehicle is transported from the assembly plant, across the ocean, and finally to the dealer’s lot. In this case, an oil and filter change may be merited.
-Coolant leak is a serious problem relating to high oil level. See Lesson No. 5.
Whatever the cause of the high oil level, the condition needs to be quickly corrected.
Note: accidental overfilling oil into your engine can cause problems too. As the crankshaft rotates it will churn the oil, causing aeration and eventually sustained foam may form. This can lead to overheated motor oil, oxidation and a loss of oil pressure. Spongy aerated oil is hard to pump. It starves the engine and critical lubricated surfaces."""""
http://www.mycarforum.com/index.php?showtopic=2650644&st=60

So I guess it fuel mix, as no contamination in my radiator.

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Added on July 30, 2012, 2:56 pm
You have every reason to change the car   even if it is 5months old

few common causes led to vibration at high speed
: 1, uneven tyres (includes imbalance tyre),
2, deformed rims,
3, problematic absorber and
4, drive shaft issue.

as you noted there is tak tak tak when you threw your car into corner, 1 and 2 are irrelevant, I have no experience in 3 

4 is safer guess and also I had experienced when the ball joint gao dim liao.

sifu-sifu should be able to give you mroe accurate answer.

Not full comparison, but just for you to get some idea:

My uncle perdana, previously change to non-ori drive-shaft. After ~2 years, the botak-ball comes out from the socket. Front tyre+rim hit the fender. Car undercarriage scrape the road. Lucky not going fast, just turning a corner within housing area. Called me for backup 

Towed to Proton Edar workshop, mechanic find 2nd hand but original mitsu/proton to replace.

Safe or not, depends on individual preference.

Depends on individual preference. A car moving >60km/h is dangerous. To me, I won't gamble my life for those few hundred ringgit. Or even 1-2k. I'll skimp on car-cosmetic, skirting, tiang-gol, or ICE or some other stuff, but not the basic stuff like tyres, brakes, suspensions, arms, engine, g/b, etc.

Maybe try check few chop-shops if got mitsu parts ?