First , if the vfo is ok and not linear. 

Tricky thing this vfo dial linearity , i have found if it is out of wack from one end to the other it is very annoying especially on 80m , mine was plus 11kc and led me to this......

Calibrate the marker 100khz crystal first , [40m band weaker station , zero beat]

On my ft200 i can remove the top VFO cover easy [4 screws] and with the cover off there is hardly any change [check to make sure].
The left hand side trimmer [front facing you] is the actual vfo frequency trimmer and it is touchy , the right hand side trimmer is the temperature compensation trimmer.

First on 80 meters dial set to "0" and centred in its adjustment range behind vfo knob [to use with cal knob] and then with [cal switch] turned on set to zero beat with left trimmer.......

Check from one end to the other [one would not be doing this if one already knew it is out of wack] and just note what is going on every 100kc's , go back to "0" and start from there and bend slightly in or out when or if the next 100kc marker needs it [i try it as it sits there a little push here or pull  to see which way it has to go then i wind the cap up to get at it better] the main both ends of the first section on the vfo capacitor , there are little sections which come into play so you will see them .

One has to start at this end [VFO cap nearly unmeshed , 80m dial "0" , because i said so :-)].

Just follow the dial up^ and follow the cap down and with patience [and no rum , rum after] and being gentle it will be done , i got mine to within 1kc or better from end to end with a small bumps 200hz to 300hz or so in the middle of the range .

A frequency counter would be good too for obvious reasons , i do not have one.

Drift , it it does from a cold turn on too much +/-1kc IN 1/2 HOUR, FIRST check the 9volts to vfo to make sure that it is relatively stable , it moves , vfo moves , if ok , temp compensation is needed .

The temp trimmer is another story as i would think it would drift differently in different climate extremes and who has maybe already been in there , mine drifts 100 -500 hz but that depends on the ambient temp here in VK as in my area it can be between 0c and 40c , the way i have set it it i keep it stable? from cold from 20c to 40c [the more common] only by fluke , it drifts towards  300 to 1kc on cold days but very slowly [like over 4/5hours ], that part and which way to trim is in the manual and it will change the "0" setting which will need readjusting ....

It does take a bit of turn off , then cool , warm up sagas , and depends on the temperature of the day when one does this , i wonder how this was done at the factory?. [i was thinking putting the ft200 in the fridge and starting from there].

If one needs to completely do the vfo for some reason , to reassemble , past the "0" or "500" dial marks either end is 2 small black lines , all one has to do is full mesh or open mesh [i do full mesh] the vfo capacitor and then align the dial black lines approximately with the pointers and do the screws up after getting the direction right .
 
Put a oscilloscope [if you have one] on the output of the vfo band pass board and turn vfo through its range and check for a relative flat constant output , this can change with age or a twiddler maybe has been there , this can be a major source of low power...low rx .
And clarifier won't centre or not enough range , check the voltage at the variable resistor and fixed resistors [also resistance] behind the clarifier knob ..

The globes always blowing , 24v ones is the go.