Probability oil leaks are creating false P codes

As a retiree on a fixed income, I cannot afford to put one dime towards this problem unless there's a strong possibility of success. Reading of the Check Engine light reveals 5 codes, all pointing to a possible transmission problem. If a transmission replacement is truly required, that's the end for this car. I am wondering though, if worsening oil leaks, particularly from the valve cover gasket, could be leaking on transmission sensors, generating a false reading. Those codes are as follows:
P0218 Transmission Over Temperature Condition
P0714 Transmission Fluid Temperature Sensor A Circuit Intermittent
P0720 Output Speed Sensor Circuit Malfunction
P0731 Gear 1 Incorrect Ratio
P1790 Not found – maybe it was really P0790 https://www.obd-codes.com/p0790
The chief symptoms of the car's recent performance are as follows:
1) Gives a slight shudder when first stopping at intersections
2) Speedometer will flutter, even though idling
3) Intermittently refuses to shift out of lower gears

Is it worth fixing the oil leaks, particularly replacing the valve cover gaskets, to see if the transmission performance improves? Otherwise, the engine seems to run well considering the mileage. I had hoped to let my son take over title on this vehicle as his starter car.