This sink was a mess when I opened up the cupboard door. The owner of the house complained it leaked.
I could understand why, the garbage disposal was mounted on the wrong side of the sink & the waste lines were ran completely wrong. The waste lines were also made up of plastic, wire, and chrome metal pipes. I never recommend using the flexible plastic lines that accordion, they never seem to do a very good job, and usually cause clogging later from food build up.
I first moved the disposal to the other side of the sink and ran all new black plastic waste lines to the wall connection, giving the waste line a direct shot to the sewer.
The faucet was old and had lost the good seal needed at the sink to faucet surface. So I replaced the faucet. (not pictured)
The water shutoff valves under the sink were original. When I went to shut off the valves to change the faucet, they no longer functioned properly. I shutoff the main water line to the house and replaced the shutoff valves under the sink with ¼ turn valves that hold up much better and shutoff easier.
Since the water supply lines to the faucet were the only thing at that point that was original, I also changed them out with new ones.
Once all the old parts were removed, the disposal moved to the other side, new waste lines hooked up, faucet changed out, new water lines, and shutoff valves installed, I water tested for leaks. No leaks found and because of the new set up, there was more space underneath the sink, and the sink and disposal drained much faster. (pictures were taken with my phone, not good quality)