Time to jump in here methinks,
I've been looking into this since the question was posed in April.
I have another interest other than 'old MTB's' and this requires quite a few pots of 'model paint'.
The RAL code mentioned above does indeed refer to what is commonly called 'Panzer Grey', its correct term is Schwartzgrau - Black Grey.
I've been digging into the various model paint ranges available that have a 'Panzer Grey' in their range.
I have produced a colour swatch card of the available colours, however I'm out of the UK for at least a week so can not post this up for all to see at present.
Cutting this short.... Humbrol 67/ Tamiya XF63 or Revell No 9 are not even close in tone.
The best I have found so far is Vallejo Model colour 70.995 - German Grey 167, I've used this on a M-737 XT Mech and its almost indistinguishable from the exsisting colour. Its worth bearing in mind that the colour on these components will have faded/darkened over time with eposure to the elements and contaminants, so this shade may not match what you have. A complete repaint may be a better option than a large touch-up. I have a pal who has just had 'Halfrauds' colour match the grey on his Ultegra pedals, I've yet to see how close the match is.
Once I finish tracking down the remaining manufactures paints I will post up my findings.
The Vallejo colour mentioned above is available in Model Zone in the UK