Do not assume anything is the first thing you learn as an auto tech so your not just wasting customers money. You need to verify that seal is leaking. Dry off the joint drive the car to get hot and up to pressure shut off and wait about 20 to 30 minutes and brush your finger under the joint, if nothing go back every 15 minutes and check again. If you can't find anything then you have to proceed with the pressure tester as the next step. Here is a picture of it to help you locate. http://www.teufert.net/partbook/67-76/0-i.pdf scroll down to illustration #6 and #16 in the diagram is the seal. If you have had a timing chain in the last 40k the best way to replace it is by removing the intake manifold. Go to the manual and follow the steps especially the tightening sequence. here is the manual from Harold Bs site https://www.firebird400ho.com/mdocuments-library/ go to the preview V-8 engine service section and scroll down to intake manifold replacement. The reason the seal is leaking is probably because when someone installed that aluminum manifold they did not follow the tightening sequence. when reinstalling the manifold you leave all the manifold to head bolts loose without heads touching and then tighten the long front bolt for the seal until the manifold and timing cover are metal to metal then torque to 15 foot lbs. and finally tighten your manifold bolts following the sequence in the manual or if none tighten in a circular pattern starting in the center and working your way out. The spec is 40 ft. lb. so do in 3 increments. Make sure you use a high temp either nickel or copper antiseize on all your bolts especially the long seal bolt as that will be a steel bolt in an aluminum intake. Speaking of that long bolt if one of the bolts is going to fight you that will be the one because of its length and small diameter and also the fact it is going into aluminum. Hopefully the previous repairer thought about the next poor guy that would have to take it apart and used anti-seize. If it wont come do not force it and break, use a torch and set the flame small and pinpoint and heat the manifold, if you are uncomfortable with that then cut the bolt leaving enough to grab hold of to heat and remove once the manifold is off. Hopefully you have verified it's actually leaking and this post wasn't a total waste of time. Good luck.