upset

I bought a 98 Civic EX, LX or DX (not sure at
this pt. not going outside) from a friend.
everything seemed fine, but i was warned
that possibly the gaskets or tranny MIGHT
cause a problem, but down the road. way
down.
specs before my purchasing: 300k miles, no
long distance
owned by owner for 7 years
Manual
Turn over is rough when gas tank is low.
Tranny replaced twice

the oil is GREAT on this car. pretty much a
champ driver. went to walmart last week to
get oil replaced, even they said it didnt need
to be and it looked great. that was 2 weeks
ago
NOW every morning since there seems to
be a bigger gradual leak. we checked oil
tonight and it was great. more than half,
nice color.  what could it possibly be?
gasket going? tranny? did walmart fkk it up?
any and all answers are BEYOND
welcomed. please and thank you.

thank you,
sarah,
a sacramento resident.