I will service '97 Disco transmission by changing the oil (not flushing)...I know that the current transmission oil is not synthetic....but I will be changing to synthetic....

1. Will the synthetic mix with the non-synthetic without causing problems to the transmission?
2. If yes, how often should I empty the oil pan of the transmission to pour more synthetic without causing problems to the transmission?....

Which one will you recommend the best.....Mobil 1 or Royal Purple?....

 

How many miles on your tranny?
If you are up over 100,000 miles, I wouldn't switch it, this could cause it to fail.
I believe you would be better of using some of Vavoline's Max-Dex for high mileage trannys and change the fluid every 15,000 miles, the end results would be better.

 

122K on the transmission....I just bought it, the transmission change gears very nice and the oil does not look darks, nor smell burned, neither produces bubbles.....but since I do not know what kind of oil the transmission has, I do want to purge the old oil (by servicing periodically not by flushing).....will a bi-weekly service be too much?....by the way....how many gears does this transmission has....it seems to go from first to third.....and then fourth (or overdrive) at +-55mph....is this OK?....