Hi,
My beloved 01 Xterra as SES light on, results from Nissan is:
DTC P0325 knock sensor, P0420 and P0430 (3 wat cat bank 1 and 3 way cat bank 2), along with exhaust manifold leaking, valve cover gaskets leaking, head gasket leaking coolant, oil pan gasket leaking, rear engine seal leaking.

The car has 194,000 miles. I have new tires, radiator, distribution, brakes, timing belt was changed at 140,000, new battery, and lot's of memories...

I'm not a mechanic and live downtown LA without any garage. I know going to Nissan is not an option. I don't really want another car, that's the one I love, the first one I ever bought new.

TJTJ suggested I post here to see if I could get some help.
The Xterra runs everyday so I could drive around.

Any suggestions?
Thanks for looking into this