Oil leak + ABS and Traction control light on olds silhoette 1995 minivan 3.8L

silhoette 1995 minivan, 119k.

ABS and traction control light on
It started after replacing the rear shocks about a year ago. ABS and
traction control light always on during winter.
In summer, it stays on after I start the engine and disappear if I stop
and restart the engine. Sometime it stays on. Any suggestion??

Oil leak
There is a oil spot under the engine. I need to add about a quart oil
each month.
Lat time I took it to a mechanic, he can not find the leak but replaced
power steering hoose and some switch of oil pump or something else I
can not recall for $200. It did not fix the problem. The car is running
fine. I need to add oil every month. Do you have any suggestion??

Please email me after removing the $$ sign $$$

Thank you in advance.