opinions - i now have a 99 gmc sierra has 125k miles and next weekend plan on doing my output seal on tranny as it does leak a lil bit...might ...

i now have a 99 gmc sierra has 125k miles and next weekend plan on doing my output seal on tranny as it does leak a lil bit...might do a tranny flush also but i have heard some horror stories about shops using too much fluid and seals blowing out..also shops use a universal tranny fluid rather than my gm trannys spec...i have the 5.3 with z71 package...if i do get a flush should i get my own fluid and have that put in or use the universal tranny fluid the shop i go to has?...my tranny still holds its power and shifts like new nothing wrong there

I would not reccomend a flush on that high of mileage transmission. If it has not been serviced reguarly I probably would just change the bad seal and call it good. If you want to do some maintenance on it the most I would do is a drain and fill with a filter change. Does it seem to work properly now? How does the fluid look and smel? If you are having any problems such as slow/soft shifts or chattering I would definatly not do anything other than the seal replacement.

fluid looks good and smells fine doesnt smell burnt....the tranny shifts fine like its new still its just the fluid levels not full due to the leak....should i do the output seal and just add the fluid it lost from th output seal leak? or a drain and fill with filter change?

Change the seal, do a drain and fill plus a new filter, no flush. Do you know the maintenance history?

If it's doing fine I'd say you can do a drain and fill with a filter change. That will take about 5 quarts. Removing the rear seal will only make a small amount come out (maybe an ounce or so).

alright....do you recomend the universal fluid the shops use or going and getting 5 quarts of my trannys specs fluid? wich i think is merc 6 idk ill look that up

I believe dexron III is what it takes. Check your owners manual to be sure.

I always recommend Servicing the transmission the correct way, which is to drop the pan, drain the fluid, replace the filter and gasket, clean and inspect the pan for debris. Then replace all the fluid if desired or just replace what was in the pan.

A "Quicky" service where they use a machine to flush fluid your transmission could cause problems later. Every transmission generates a some wear which is collected in the pan and the filter, when power flushed this debris can be forced into places where it can damage your transmission. Also, if your transmission has metal or clutch material in the pan (whick in an indication of problems to come), a transmission pro will know this whereas a quick lube place will likely not.

Its always a good idea to change the ATF. It will not last forever.

I disagree with the don't flush responses unless a trans has not been maintaned or the fluid is burnt or shows signs of metallic color from clutch disc. You should use the correct fluid or better that is listed in the owners manual. Modern flush machines will not cause a leak as they are powered by the ft pump in the transmission. I strongly recomend flush over drain and fill as when you flush you get all 12-13 quarts of old fluid out versus 5-6 in the pan.

I purchased a Dorman deep trans fluid pan. The interior is powder coated along with the exterior. I am a bit concerned that the powdercoating inside would eventually degrade and send fragments into the transmission. Anyone have experience with this pan?