My 99 Si had a couple of oil leaks. Replaced the vtec seal, vapor canister seal, and oil pan gasket. But I'm still seeing a good amount of oil leak right in the area on oil pan where the tranny meets the engine. Could this be the rear main seal? Is there any way to fully check where the leak is coming from?

 

I would look into rear main. However, I had a transmission with a blown ISB so bad that leaked trans fluid in that same area; took my clutch with it. I assume you're okay in that regard, however. ;P

Clean it all up and see if you can pinpoint where it's coming from, easier when the engine's not covered in grime.

 

x2...definitely clean it up so you can get a clear idea as to where the leak is coming from. I have had leaks in the past that appeared to come from below, but actually started from above. Purple power and a pressure washer will do the trick. Just make sure the motor is cold.

 

I've cleaned it up twice, but can't figure it out. The transmission is not having any problems and I don't see any leaks from it.

 

Had same issue rebuilt my motor and put everything spankin new seals n gaskets so wen the time came to fire it up everything was still fine no leaks it wasent until I drove it that my tranny would leak between block n tranny case so I thought it would be rear main seal n it wasent turns out it was the trannys intermediate shaft seal

 

Hmmmm...where is this seal on the tranny?

 

the input shaft bearing is in between the engine and the transmission where the clutch or torque converter would be at

if that were the case you'd have tranny fluid on the ground

although the rear main is the probable cause, check uptop for a leak at the distributor and vtec solenoid gasket cause it can flow down to the same spot on the ground

 

I didnt know either so I called my mechanic he explained to me dat in order to get to dat seal u have to open up the tranny case ill find out til monday since he is on vacation for da holidays, keep in mind im not tellin u dis is da problem in ur car just letting u knw wat my problem was

 

I already replaced the vtec gasket and have killed all the other leaks. this is the only one left, but I'll double check everything.

If the leak is within the clutch/tranny area, I'll be putting in new main seal, clutch, and imput shaft seal just to be safe.

 

You have to crack open the tranny case to get to it? From there does it leak then?

 

When the seal wears off oil finds its self through and eventually leaks u wont see the seal unless the case is apart

 

5 speed transmissions have the ISB seal under the ISB on the inside of the case. You have to remove the input, countershaft and gears to get at it. You also have to remove the ISB which you'll probably ruin in the process, so make sure you get the bearing and the seal or you'll be waiting for parts. The automatics are on the outside of the case (OP has a 5 speed though)

Btw, you might also wanna check the distributor O-ring, sometimes that can look like a an oil pan gasket or rear main seal leak.

 

to replace the input shaft seal? yes, if its more than you want to bite off, if its not leaking, leave it alone