My dishwasher has become very slow to finish, often not draining fully?

The dishwaster is slow to complete its cycles, often not finishing the drain part. This morning it was showing 0 mins remaining, yet the motor still sounded like it was trying, and there was water left in the unit.
Often a small amount of water seems to be leaking too - although its so small it doesn't reach further than under the machine (I see the wet when i pull the machine out.

Its a Hotpoint DWF61, freestanding. Approx 7 yrs old. I have checked & cleared the drain hose. It seems to pump fine when checked. Some mornings its washed fine too. Although its always slower than anticipated (ie 2 hour wash might take 4 hours).

Finally - when filling it often 'thumps' as though the water is being turned on & off abruptly every every 1 or 2 seconds. Leaving the power off between washes *seems* to help?

Any thoughts? Can I investigate myself? I have taken the door & side panelling off, but am not too sure what I am looking at :-)