yeah, lack of driving is a killer for anything rubber... Dont exactly know why though, but you're talking to a 16 year old who has 3 cars... 2 of them sat for significant periods of time (truck=3 years of "hauling stuff only", benz sat for a long time...)
both of them leak.
Best thing to do (other then drive more) would be to replace all of the fluids with premium ones (mobile one delvalc, royal purple... full synthetics all around)... Use the good filters too, and you can go with changing the oil once every year, and for the other fluids (brake, power steering, antifreeze, transmission) flush them (except the trans, just drain that one), and then flush them again in 4 years...
That would be one way of helping the seals in your car... dont know if anybody else has other reccemendations.
I used full synthetic engine oil in my 82 f150 (for 5000 miles)... NOTICABLY less leakage, and it ran a little better... Went for the cheap**** oil (1.29 a quart) and it's leaking pretty bad again
I'm a firm believer that using synthetics is ALLWAYS a good idea, and wont "clean out" the sludge sealing the engine... I dont think it's possible to seal an engine with sludge, and if so, you've got more problems then fluid leaks
Anyways, good luck with your car, and welcome to the forum
~Nate