I have 100k miles on my 2002 WRX. At around 30k miles I changed my tranny and rear diff fluids to full synthetic. Now, I'm doing a huge maintenance project on my car and was wondering if it is ok to put in new tranny and rear diff fluids, or if it's better just to check the levels and keep the old fluids.

This brings me to my second question...as part of the big maintenance project I'm changing the timing belt and was wondering if I really had to change all the following parts or if I could just change some of them and be fine. And if I don't need to change all of the parts which parts should I change for sure.

13028AA181 Timing Belt
21111AA007 Water Pump
21114AA051 Water Pump Gasket
21200AA072 Thermostat
21236AA010 Thermostat Gasket
807615081 Bypass Hose
806919050 Oil Pump O-ring
806733030 Crank Seal
806732150 Cam Seal (x4)
13594AA011 Timing Belt Cover Sling (lower)
13033AA042 Tensioner

Thanks all for any input you can shoot my way!

--Joe Kwon
2002 WRX