dual cs-502 problem Help!

Hello
Unfortunetly i can't speak german so i will write in english

Recently i've bought my first turntable - dual-502 on internet auction service.
Much anticipated package came to me last week and everything seemed ok at first.Turntable played nicely and was in good condition...for one hour.
Then it began to brumm very loudly,which also afected sound.After "investigation" i found out that the source of this sound was motor.
I checked the turntable next day and it was the same thing - everything ok and after 45-60 minutes the motor was hot and it started to brumm.
I read on dual-reference site that lubrication could help.
So i dimounted motor and oiled it but it didn't help.
And what's worse turntable slowed a little so the vocals are unnatural now and songs last 15-20 seconds longer.
But it wasn't the end of my nightmare.I thought i've mounted motor incorrectly so reapeted whole operation few times.During that I found out that placing "the thing attached with two little screws"(antriebsrolle in german i think)lower stops brumming.
The problem with speed remained.I left turntable for a night and next day and...

it started to play terribly.Music is almost unheard and unclear because of the noises coming from the speakers.I think it is "arm problem" because now it has tendency to slide through the LP to the center(left) or to the "start point"(right) with arm balanced the same way as before problem.So now i have:
1 brumm
2 speed
3 arm
problem
Can this things be correlated?Is speed problem because of brumm problem?Maybe i gave too much oil?And most importent thing - what to do with the arm?
Could someone help me? I would be grateful for any tips.

Hi Dual Sammler
I'm pretty sure that this noise is coming from motor.It's just some part of motor touches something while turning.Friction thing.
As i said i managed to "repair" this but this "repair" could caused turntable playing slower.But with this problem i will be handling later.

For now my main concern is arm.I really don't understand this.Everything seemed alright,it played well with or without noise from motor.And now it "runs away" from LP to the left or right and the turntable plays terribly.I know it isn't matter of balance cause previosuly even unbalaned arm played better ,still the arm doesn't "stick" to lp now.
What could be the problem?As i said it is my first turntable so i'm still learning.Is it catridge or needle problem(is it possoble that catridge moved slightly all by himself) ?Or some kind of arm defect?
I think that this kind of problem should be popular so somebody must know something.
Any tips?

Hi Einsteiger
I'm pretty sure it isn't matter of balancing the arm but i checked it again.And even with the stylus pressure=3(maximum) and arm balanced the way that needle stick to the lp strongest as possible ,it is the same thing.When playing song at the end of LP ,arm slides to the center.
When playing first song arm slides to the right.The stylus touches the lp(strongly) but the arm simply moves.
As i said i balanced arm before this problem occured and everything was ok.With too much pressure it played "muddier" ,with too low - high tones were dominant.No i can hear only middle songs and quality is unlistenable(so i assume even then the arm has tendency to slide).

The stylus pressure and arm balancing work ok.
As i said i'm new to this.Could this be antiscating defect?
or catridge ?or maybe stylus?