I replace the front axle on driver side of my suzuki Esteem but started to leak transmission oil pretty bad. I was told that I might replace the output shaft seal.. What could possible happened?

not told what leaks and to where.
we can no see leaks blind in text box.
axles?
autotrans
manual trans.

cause are only 3.
bad gaskets and seals
overfilled. (never do that)
or on ENGINE ( )PCV valve clogged and engine pushes oil out
rear main seal and to the TC and bottom bell housing leaks oil
and is not the transmission, leaking. fooling owners.
oddly
other causes, 4wd axle vents clogged with mud or bug nests>

no engine told
no transmission told at all(options day1 new car)
RWD
Front; with Mitsubishi R4A51 Transmission
or Front; with Mitsubishi V4A51 Transmission

When it is low to the first mark you need one US quart. The engine requires 5W-30W oil.

get the VIN/chassis number, part store will know how to match it up.

you need and expert mechanic to look and access this damage.
its non trivial.. and if not investigated proper can be very dangerous.

if really curious of all the long steps to do this,
alldata.com is your ticket.

Step by Step:

1. Remove tire
2. Remove cotter pin / lock bolt in lower ball joint
3. Remove Tie Rod End nut.
4. with a 32 mm socket removed large axle nut (air tools will most likely be required for this stage)
5. Seperate the tie rod end from knuckle
6. Seperate Lower Ball joint from knuckle
7. Pull knuckle back while pushing axle out of the bearing
8. Pull axle to the side so you have enough clearance to pull right out.
9. Pull axle out (will be stiff as there is a c-clip holding it into the transmission) take your time!. Sometimes a sticky axle can be freed from the transmission with some prying between axle and transmission.
10. Replace axle.(make sure axle is seated fully into the transmission)
11. Re install all nuts, and cotter pins.
12. Make sure you torque your axle nut to 90 ft lbs. (CRITICAL!!) - Too tight can cause premature bearing wear, Too lose and bearing could seperate, and possibly loose the tire while driving.

On the Esteem 1.6L: the Crankshaft Position Sensor is located on the right side (passenger side) of the engine Oil Pan.

For the Esteem 2.0L: the CKP is located behind the engine Flywheel in the back of the engine block. It is necessary to remove the transmission to service the sensor.

its just the seal. not the axle.

I would say that you should have replaced the seal as well, sometimes they leak if they have been disturbed

CV shaft replacement needed cliff

I have 1998 Maruti Esteem Automatic gear car - It works smoothly for 10-15 Kms and afterwards gear not shifting (may be getting heated inside somewhere?) - Recently I changed gear oil also. Any solution???