2007 F150, 4.2 V6, 98K miles, PP 5W20

After about 1500 miles I now have an oil leak. I can press on the plate that divides the engine from the transmission and oil seeps out. It also gets on the sway bar and drips onto the ground. I'm thinking rear seal. I was going to try a HM 5W30 oil but want to see responses from here first.
The oil has always been changed with MC 5W20 and MC FL-400S filters every 3-6K miles.

 

Changing the oil type at that much mileage is always a risk. Go back to the MC oil and it will likely deminish. Otherwise it may just need a seal or two.

 

it would have leaked no matter what.

A heavier weight oil may slow the leak but it will only delay the inevitable....

 

More than likely it's a leaky seal. You MIGHT be able to stop or slow it down with a High Mileage oil. Pick a name brand one. There's more to HM oils than just viscosity. They also include more seal swell agents for leaky seals. Or you can change to G-Oil at the next OCI. It's polyol ester base has great solvency and is great for taking care of seals. The current formulation is the best on the market so if you use a synthetic, this one tops the list.....for now.

 

Check the obvious...

Check your PCV valve, which is located in the rear in the valve cover right valve cover, if you are sitting in the driver's seat. Might've popped out or there is something wrong.

Check your dipstick tube.

Check your valve cover seals for leaks.