A few weeks ago i did my rear main seal,i took out rear cap cleand up a bit replaced seal and put her back together, now, i have a bad knock and low pressure. When i first started it it ran perfect and drove it about 500 miles before lost pressure and got noises. So I bought a used 4.0 for real cheap it has 80000 miles on it and i want to put a new rear main in while i have it on the stand but im afraid ill F--k it up again or have the same issue..What could have gone wrong?