Hi Ian,
The ink may be washable and come out with ease, but the first thing to do is to take control of the spill.
The ink may have penetrated deep into the pad - if so, to attempt removal without isolating this reservoir could make matters worse.
If you have access beneath the face fabric, first insert a thick absorbent pad between the pad and fabric. the next stage is to prevent lateral wicking of the spot. this can be done with a barrier substance such a glycerol, or simply by wetting around the spot.
Next select the spotting agent. The choice may be limited by the tolerance of the fabric to water/volatiles and by the dye stability - this will have been determined by your initial tests.
Suitable agents may include water-based (e.g. Stainpro), alcohols or alcohol-based (Isopranamol or Echo Spotter) or aromatic solvents (Solvex). whichever you are going to use, apply with an absorbent cloth, working from the outside in-ward.. Use clean section of cloth once soiled and do not forget to change the inner 'barrier pad'.
An alternative approach when using a water-based spotter is to have your upholstery tool sucking from underneath, whist applying the spotter from above.
Whatever method adopted, it may be advisable to also treat the pad surface to remove some of a heavy deposit and also on completion, to place a sheet of plastic between pad and fabric to prevent later up-wicking
