Washing machine problems?

The washing machine stops before it has reached full cycle- I have to turn it off, turn the dial round again full turn and then switch it on again and then it does the final spin but still stops short of completion, leaving clothes that are still soaking wet and water left in the drum. I tried to check the pipes- couldn't open the U bend pipes under the sink but unscrewed the pipe leading to the washing machine and noticed it was gunged up with gungy stuff- smelly too. Think the water maybe blocked by pipe blockage- may not be able to spin out properly. Also, when I run the tap it takes a while for sink water to drain. I could get a plumber to unblock pipes/drain but would that sort out the problem with the dial- is it stopping short of the full cycle because of the drainage problem or is it just faulty? Is a dial expensive to mend? Is it time I got a new washing machine or is this just a drainage problem?