1. Will not damage paint Dot 3 brake fluid will.
2. Perception that since Silicone will not absorb water it is less 
corrosive to calipers and wheel cylinders. 
3. Will last longer in cars used only occasionally.
4. Higher boiling point.

Most web sites I read recommended agaisnt Silicone fluid in brake 
systems built for Dot 3 type fluids. Here's why:

1. Silicone may damage seals in system compatible with Dot 3.
2. Silicone will give you a mushy pedal as is is more compressible 
than Dot 3.
3. Although water is immiscible with Silicone any moisture in system 
will sink to the lowest point and water will be suspended as droplets 
within the silicone and can still cause corrosion or since water is 
in droplets then the water may boil and resulting steam may lock 
brakes periodically.
4. Silicone must not be mixed with Dot 3 so if used system must be 
flushed with alcohol and dryed out with air.
5. If used frequent bleeding is recommended as air will also form 
trapped bubbles in system. Just pouring fluid too fast or shaking up 
can of fluid can cause trapped air.

After considering all things and bleeding my old system and getting 
clean fluid with no rust or milky appearance, I am going back with a 
typical brake fluid (glycol base) with one twist. 

I contacted Castrol by e-mail and also got confirmation that Dot 3&4 
fluid is compatiable with older systems. The Dot 3 & 4 brake fluid is 
also gylcol based but has higher dry boiling point in 450-500 deg 
range and also higher wet boiling point in the 290 - 320 deg range. 
Castrol's Dot 3&4 fluid is called Castrol GT LMA. The LMA stands for 
Low Mositure Affinity. Valvoline also has a Synetic Blend Dot 3&4  
that is glycol based and has high boiling points. I plan to use the 
Valvoline as it has slightly higher boiling points than Castrol. I'll 
let everyone know how it goes I use my 63 Avanti as a daily driver 
and put 7000 miles on it last year so the car will not be sitting up 
for long periods of time.
 
John Graham
63 R1 (R-2386)