Used this method to fill the transmission and rear end on my 1988. It worked like a charm. Just take a look at this link: Changing The Transmission Fluid - The Easy Way

 

Congratulations,only 10 posts and you are already listening to the "Guru of Rotary"!..(Aaron Cake).
He is one of the Veteran Moderators here,and an All around Good egg!

 

I may be old, but I guess I'm not all that stupid--at least I hope so. I'm looking forward to spring when I can see if the things I'm doing over the winter actually help the stuff that have been driving me crazy for the past three years of RX7 ownership.

 

Gear oils, all fluids for that matter, seem to be overlooked alot. I try to do gear oil every 25k or so. Brake fluid every year or two or when it starts getting dark. I change coolant out every spring...kind of a routine with other stuff when it comes out of storage.
BTW, I'm in Bellevue and likely older still. What is it that's been driving you crazy?

 

Really three things have been bugging me--a crack in the left rear tail light I haven't found a suitable replacement for, 3rd gear sncro that scratches once in a while, and the driver's side window switch that doesn't work for the passenger window. We bought this vehicle after 3 years of looking for a 5.0, 5 spd. Mustang convertible and never finding one. We bought it from the original owner with all documentation including the original owner's manual and window sticker. A month after we got our RX7 we found an unabused red-on-red Mustang convert so have had two red convertibles for the past three years. We've thought about selling the RX7, but don't want it going to a youngster. It's just too nice a car. (I'm 67 and have been detailing and showing cars for years.)

 

Well, you have me by a few years.
As for the issues, none sound all that serious...with the exception of the synchro. Maybe your fluid change will help that...at least temporarily.
I don't know the FCs all that well, but seems like I hit the local 'U-Pull-it' lots every couple of months in an effort to keep my daughter's car on the road (last year at NU). Occasionally I see FCs in there, in fact not long ago I saw a 10th Anniversary. Just something to keep in mind as a source for all the random bits like a window switch and tailight...if you haven't already.
Not surprised it was hard finding an unabused versions of either car. Both sound like fun, but glad you kept the 7 too. I hit the Coffee Cruise (organized by the Mustang Club) a few times during the season. Maybe we'll see you around.

 

Took a few trips to U-Pull-It and others to pick up some small stuff, but have been unsuccessful finding the 1988 tail lights and switch locally. Our RX7 spent a good deal of its life garaged under a cover so the parts I have found have been in worse shape than what I have had in place. Last weekend we installed a set of beautiful 1991 tail lights and I'm currently waiting for a switch that I bought online. Hope it is as nice as the tail lights.

Next winter job will be putting new electric window regulators in the rear side windows of the '87 Mustang. We've had a '91 and a '90 and they have all had some of the same exact issues. However, the nice thing about the Fox bodies is the long manufacturing run which means a great availability of NOS and repo parts. Ours is also a 60K mi. car that spent a great deal of its life in Arizona so doesn't have too many issues besides a case of acid rain on the paint.