I not familiar with the 24” model, I’ve only played with the 16” model. I’m assuming that they are similar.
The planner tables lift off easily, there is normally two hold disn clamps that secure them / allow them to be pulled back from the cutter. When lifting off, there are metal pins that stick into a groove that the beds are guided by when sliding back. It’s important to lift the beds off verically rather than sliding to avoid damage.
With them removed access to all of the gubbibs is really easy. It’s proper engineering and everything is very easy to adjust. You will probably find that the two rollers in the thicknesser bed are both jammed in one position and won’t rotate. Usually they are just full of rubbish and need a wire brush and some white grease to get them moving again. The rollers should protrude a smidge above the bed. If you place a flat board on the bed and push whilst raining the rollers you will so be find when they are just protruding as the board will suddenly move easily. Very very useful for heavy wide stuff.
Have a look at the serrated roller that pulls the wood through the thicknesses. Again the serrations will probably be full of gunk. With the planner tables off, cleaning it out is very easy. Check that roller is reasonable straight and dies not have a hollow in the centre where most things will been fed through. Not a big deal if it is, just remember to feed stuff through avoidibg this area if it’s not too wide. Wide boards that span it will be pulled through anyway by the part of the roller that’s in contact.
The Dominion has four supports one on each corner of the thicknesses bed each with its own grib. Check that each is supporting and isn’t loose through wear. If any are loose it can cause the table to tip slightly. Tighten up the gribs as necessary. The beauty of these machines is that just about everything is adjustable and designed to allow for wear.
The gear box that drives the serrated roller is separate to the motor. Check it’s turning and if it’s not been maintained (virtually all wood working machines aren’t, change the oil)
Check the belts, the rear cover comes off to reveal all of the belts, usually two bolts either side (about £20 worth). The belts are easy to replace and as a matter of course should be changed. They will have become hard and probably cracked. This increases vibration and wear as well as reduced grip on the pulleys that can lead to slipping. Whilst changing the belts check the tension pulleys move freely, again they can have become still and no longer move freely again causing slippage of the feed roller.
Finally the machine should have two blade setting jigs that are stored mounted on the rear of the infeed table. The plane blades sit on springs, you just screw the jigs onto the spindle (taped holes exist) and they push the blade down to the right height, tighten up the blade very securely and it’s set. Very quick and very very easy.
With all of this done it should eliminate any problems your having.