recently purchased this vehicle good solid lump in it 120 k miles
only issue was this vibration problem above 50 mph that got worse after 1000 miles of using the car ....but .no worse under braking
had the wheels balanced ..no joy
had the tyres replaced and re balanced ..no joy
from another x type that had no vibration issues swapped all the rims /tyres on to my car ....no flipping joy !
replace the front discs /pads ...No Joy
starting to get a little concerned i had purchased some ones major problems ...its where do you stop spending on a car of this age ? as it has a limited ceiling value wise.

thought i would put it through an mot test .(only came with 8 weeks mot on it ).if it failed and needed big bucks to get the new ticket on it ...then its time to cut my losses and scrap the car .
good news passes with only £80 to put a few bits right once i had the new mot i mentioned the vibration issue to the chap at the garage ..he carried out a check under the car on things that dont cause a mot failure ... told to get my wheels checked out ,,, really ?.Did not tell him the long sorry story of all the things already tried .

ok lets escalate this to the next level (and the last one i was going to invest any more money in .

purchased both front drive shafts and replaced them ,I could have done one at a time to save buying both. if the first one did the job ,but i was now at the do or die stage with this one ( nb its a lovely straight /clean /tidy car ) or i would have just resold it early in the game and passed the baton on to someone else to solve the problem..
test drive ..fingers crossed ,, vibration is no more
nothing obvious wrong with the driveshafts on a quick inspection ...But on a much closer look the problem became apparent ,,nearside drive shaft (the long one) has a supporting bearing /rubber mounting mid way down the shaft .had to look very closely but upon doing so almost ALL of the connecting rubber sections had broken off . put the shaft in the vice and could almost twist off ..It must have been kicking like a mule as the speed built up !
car now is driving lovely .
Sorry if the story dragged on a bit but reading it and if you have vibration issues it may well save you both time and more important wasting good money .drop the engine tray off and really give it a through inspection
hope this helps someone out

 

Glad it worked out for you!