I'm having power to throttle ratio jerking and sluggishness issues in my 2005 Forester.  I have a 5spd manual transmission.  I know I have an Oil Pan Gasket leak and some belt slipping which I hear as an squeak especially when the AC is on.  What are some trouble shooting methods and or obvious 

Maintenance I can do to resolve this issue? 

They may have changed, but as far as I know Subaru doesn't use Oil Pan gaskets.  They are Silicone Sealant.  I've heard you can pull the pan while the engine is in the car, but it's a lot harder.

 

As for the other issues, the AC is probably due for belt replacement and so is the power steering/alternator belt if it  hasn't been done already.  You might be able to tighten the tensioners, but this just buys time and doesn't correct the problem.

 

Regarding the power issue, when were the plugs done last?  If that has wires (and not coil packs) when were they last changed?  PCV Valve Changed?  Fuel Filter, and Air filter changed?

 

And how many miles are on the car?

 

And, since you know you have a leak, is your oil full?

oil pan gaskets rarely leak - you might do some extensive cleaning to try to confirm the leak's location.

 

is the check engine light on? get the codes read and post them for us.

 

are you feeling a jerkiness after the transmission has warmed-up? will the car do tight circles on dry pavement smoothly?

 Spark Plugs and wires, Fuel filter, air filter. Is the check engine light on? Check belts for ware and proper adjustment.