Bosch S510 dishwasher - how can I fix it?

Machine has worked OK for 26 years.
Yesterday, it just got in to the washing cycle (brush symbol), when I heard a clunk then it fell silent.
I had to manually nudge the program wheel a few times to get the machine to complete its full cycle.
In the first part of the cycle, water had appeared and was seen welling up in to the sink , but when the dishwasher was eventually opened, no water appeared to have entered the dishwashing chamber at all.
I would like to keep the machine going if I can, but I will not call a man out (too expensive) and don't want to spend a lot on parts unless I am pretty certain of success.
Can anybody help please?
Regards
Mark.