front passenger side wheel problem( blew out grease cap off hub on motorway)

 Hi 
 whilst on my way back from North Wales a 300 mile run in 300 gd lwb 460 wagon, the wagon suddenly pulled to the left and made a noise as if  something had released alot of air(as if the tire had burst) whilst traveling at 60mph, i managed to control the wagon and continued home as i was about 7 miles away and it was 3 in the morning did not really want to get stranded on motorway- the wagon seemed to drive ok all the way home. On arrival i checked front passenger side wheel, the wheel was fine but i noticed that the grease cap which fits where the centre locking nuts are is missing along with the merecedes alloy wheel centre cap, and there is some brown grease showing. The Locking nut is visable and looks like the locking nut has moved from where it was locked in with locking washer by a couple of millimeters as it is no longer locked with the washer.

 Not long before i had carried out a complete full front axil service on the front on 300GD. New swivel ball seals plus 800g of grease in each swivel ball. New CV boots both sides as they where broken and CV grease was leaking from the swivel balls, bearings all seemed fine( did not replace them). There was movement on both front  wheels, it turnred out drivers side neaded a new CV joint as the treads had worn and the locking nut was not tightening, passenger side seemed like the king pin had play in it, so i added shims whilst carrying out the service( 1 on top and the other one below). The locking nuts have been tightened to 200Nm torque ( had to use a bar on torque wrench). It has not been  that long since the service, i must of drove the wagon a few hundred miles and no real issues , checked for play in wheels and everything seemed fine no movements no leaking swivel ball. Topped up the driveshaft oil 85w 90 hypoid until it started to drip from the fill hole front and back only needed about 200ml each.

 Has anyone experenced this before? and does anybody know what might of happened here? likley cause?. Im guessing there was some pressure/grease build up which has caused the grease cap to blow off along with the centre cap on alloy wheel. I filled each swivel ball with high velosity grease about 800g each side. I did add 2 shims to the king pins 1 on the top and 1 on the bottom( not very thick at all cannot remeber the size). I did notice that one of the caps on the king pin bearings was missing  which i did not replace left it as before. I did tighten the locking nut to 200NM and waited for the wrench to click- the torque wrench i used only went to 210Nm Max, , so i dont think they have been tightened any more than they should but did have to use a extra bar on the torque wrench to achieve the 200Nm.

 I am no fully quailfied mechanic, i have had some guideance but this is the first time i have worked on G class- i have had the G wagon serviced when i first purchased it  by a independant mereceds specialist- for a major service, it had a oil and oil filter change,and second hand lifter pump, greased all p/shafts and suspension and he charged me six hours labour with a bill well over £450 and said he checked the G wagon all over and that it was all ok in good order. It was only 2 months later (about 1000 miles) when it went for the MOT it failed due to movement in the front wheels at 12/6 o clock. plus the swivel balls where leaking , the brake caliper was also loose on inspection, it was also apparant the mechanic did not even check the brakes, he never took the wheels off, never checked the rear drums- because of this i have lost  faith in mechanics/garages and have therefore decided to learn as much as i can and carry out the services myself such as oil/ filter/fuel filter changes etc. In total i have done over 6000 miles since owning the G wagon in 2011. Its not quick at all but manage to run 60-70 on motor way without much problem slow going up hill but guess thats what the 300gd NA are like, i do give it some  - it is clean the seats are all in fantastic condition along with the carpet, roof lying. Engine/ engine bay is also very clean, it aparently sounds good, its only showing 59600 miles present on the clock im not sure if its has gone around the clock. This is my first wagon and first diesel its old as its 88 F reg but i love it, im abit of a perfectionist and am trying to give it a once over for peace of mind as this was the whole point of me taking it to a merc specialist and sort out any niggly bits.. So far it has been a interesting experence!!!  enough said ...

 To the point can anyone please advise what issue i could be faced with here.