20 hp kohler leaking gas out front right side of motor

pull the carby and recondition it with a new kit including new needle and seat assy
put a small in line fuel filter in the hose to stop dirt/ straw getting into needle /seat and not allowing it to shut off

Check your connrctions. May have to he surface alittle

Sounds like you got some dirt or rust in gas tank
try emptying the tank and cleaning it out. also check you bottom of you gas can too it could be souse of dirt in you tank.
Just remember to put fresh clean gas in mower gas tank after you clean it.

Do you hear the fuel pump running? Is there gas coming out of the pump? Could be a bad wire connection to the fuel pump or bad ground connection.

Have you tried pulling the hood off cleaning any oil contamination off the suspected area then start it and watch while it's clean. It seems weird that a valve cover gasket would be the failure after two repair shops looked at it. You may need to look close at the head gasket could possibly being blown forward. I know you said it leaks so I'm assuming there is nothing actually coming from within the motor being blown through the muffler I have seen these motors burn oil heavy on startup than clean up after warm.

to be honest the enigne ahas a control that the left side must fire and run before the right starts to fire it sounds to me like you have a fuel issue possibly the carb. is gummed up and dirty.

first job is to check the part load and main beather hoses are ok the stability system light may be a false indicator if the engine has stalled best is to get fault codes out of the ecm with a code reader to help but air leaks on the engine inlet side can cause strange/seeming unrelated symptoms

Sounds like the float in the carb is leaking by the set.

Ever try draining the carb ? it may have sediment in it.

1989 Kohler 20 backfires through the exhaust. What are the possible causes?