G,Day sgblazer2. The O ring wont affect the performance of the hydraulics as such it may allow unfiltered oil to go through the pump but that would be all . You say the draft top link does not move at all I have never experienced that in all my 36 years working on Masseys ,you did have the brushhog on when you tested it ??. To remove the draft control spring assembly, step one is cut or remove the rubber boot ,it will be no good anyway,and it gets in the way when you are removing the adjusting nut. replace the rubber boot during overhaul Undo the small allen headed grub screw that locks the adjusting nut in place ,the grub screw can be found on the right hand side of the lift cover adjacent to the adjusting nut, undo about one /two turns Make sure you use a good fitting allen key . Next step is to spray lots of your favourite release oil,, LOTS. if you dont have the tool to undo the nut get a fairly large chisel and dull the sharp end on the grinder and use it on the thin part of the adjusting nut ,go back and forward till it starts to move ,this could take some time I have on occassion had to heat the nut red hot to get it to undo if you do use heat dont put water on it when the cast cover is HOT you will crack the cover. When you have the assembly out give the lot a good wash in petrol and look carefully between the u shaped yoke ,there is a rubber plug in there remove the plug and you will see a cross shape on the end of the shaft with a locking pin going through into the housing this stops the shaft turning,knock the pin out with a pin punch. Next try to undo the shaft using the cross on the end of the shaft again plenty of release oil and maybe a bit of heat. next clean everything up a wire wheel on the bench grinder is a good tool wear goggles and a mask and give everything a good clean ,dont forget to clean inside the lift cover where the spring assembly fits, be carefull there is a large support washer in there right at the end ,it has the draft sensing rod sticking throught it this is where the hydraulic system READS the movement of the linkage,once cleaned out and the large washer has fallen out GLUE it back in place with a big dob of grease . dont forget to give the thread a good clean with a wire brush. Next reassemble the draft link assembly ,same way as you stripped it again using the cross on the end of the shaft ,This part is important ,Tighten the spring by tightening the rod or should i say undoing the shaft until THE SPRING IS JUST NEAR IMPOSSIBLE TO TURN BY HAND NO MORE then line up the locating pin hole and knock the pin in. Plenty of grease on the adjusting nut and the thread in the housing, make sure the big washer has not fallen down then fit the assembly . Next again this part is important some think that by adjusting the spring all the way in is good this is not so and can affect the internal adjustments as has been mentioned in the previous post ,Install the assembly and ADJUST THE NUT TILL THE SPRING ASSEMBLY IS TIGHT AND KEEP GOING TILL IT STARTS TO RATTLE AND BECOME LOOSE AGAIN AT THIS POINT UNDO AGAIN TILL THE ASSEMBLY HAS NO SLACK,Lock the allen grub screw and reconnect the two yoke bolts . That is the draft top link adjusted . refit the implement and try you will see the draft toplink extend about 1/8 th to 1/4 inch depending on the weight of the implement,again set the draft lever all the way back and leave it there ,using the position control and if the hydraulics are all good the three point linkage will respond exactly as per the movement of the lever example move the lever UP a little bit and the linkage will raise a little bit and STAY THERE and so on. Set the response control lever ,on the right hand sideplate next to the transmissoin oil dipstick by raising the brushhog to the transport position and setting the response lever t o the SLOW position and then lowreing the position control lever you may find that the linkage will not go down SLOWLY move the resonse lever towards the fast position until you are happy with the rate of drop,incidentally this rate of drop will also affect the response of the brushhog i.e how fast it responds to up and down movement on uneven ground ,you may want it to respond faster ,you know how to do this. thats all . It has been suggested that you can use the draft control lever for the brushhog ,using the draft lever will not give you positive response,the correct way to operate is to use the position control . Happy Days Hutch.