Just went through this with my car.
new parts, never any exposure to DOT 3 or other. New lines, rebuilt Master by Apple Hydraulics. Rebuilt booster and rear proportional valve and distribution block by Steve Gregori at BrakeBoosters.com (pre Mike Gibbons).
All new lines,seal etc.
Pressure bled system with DOT 5. Great, firm pedal.
Car sat (not driven) for ~2 months and noticed a puddle under the frame where the booster-MC is. Bottom of master was wet and a drip was hanging from the rear proportional valve.
Pulled the master and PP valve. Disassembled and all the seals looked good. No swelling or deterioration seen. Looked at the bore of the brass sleeved MC and it had some what I consider rough cross hatches from the hone operation. I was not happy with this and took some 2000 grit paper and polishing compound and worked until a mirror finish on the seal surface.
Opened up the rear PP valve and saw a scratch along the seal diameter about 0.003 to 0.005 deep. Definately a leak path. I took a sanding tootsie roll and carefully worked this out, blending about half way around the diameter. Then polished the entire diameter. Re-assembled and pressure bled. 3 months later not a drop from anywhere. Pedal is good.
The bottom line is, in my estimation maybe DOT 5 is more prone to imperfections and sealing surfaces have to be very good. I was disappointed at the workmanship on the rebuilds, but maybe they would have been OK with DOT 3. Don't know.
I know the rebuilders don't like DOT 5 and maybe its due to the above. I do know that if you spill DOT 3 or if the rebuilt part leaks and damages an expensive paint job, will they reimburse you for the paint work? I think we all know the answer to that. It's just not worth the risk to me. If I had used DOT 3 and it leaked as the 5 did, I would be out thousands in paint repair to disamantle and pull the subframe to fix it. If you have a driver level car and you are not worried about having good paint, go for it and use DOT 3 (or 4 or 5.1).
I now categorize any rebuilt-restored part as an engine rebuild. Get good folks doing the work, but trust that no one did the job right. When assembling your engine, verify that all the machining was done correct and that all clearances are correct.
When I was contemplating using DOT 5 I read about every post I could find on the subject and it ran about 50-50 on folks that swear by it and folks that swear at it. Nothing absolutely definitive one way or the other.
FWIW here is the fluid I used:
https://www.amazon.com/dp/B002IAS82W?th=1
I'm not going to say it's the best out there, but it works for me. There are higher priced ones, but when you compare the MSDS's they all seem to be the same as the Johnsens.
Good luck.
new parts, never any exposure to DOT 3 or other. New lines, rebuilt Master by Apple Hydraulics. Rebuilt booster and rear proportional valve and distribution block by Steve Gregori at BrakeBoosters.com (pre Mike Gibbons).
All new lines,seal etc.
Pressure bled system with DOT 5. Great, firm pedal.
Car sat (not driven) for ~2 months and noticed a puddle under the frame where the booster-MC is. Bottom of master was wet and a drip was hanging from the rear proportional valve.
Pulled the master and PP valve. Disassembled and all the seals looked good. No swelling or deterioration seen. Looked at the bore of the brass sleeved MC and it had some what I consider rough cross hatches from the hone operation. I was not happy with this and took some 2000 grit paper and polishing compound and worked until a mirror finish on the seal surface.
Opened up the rear PP valve and saw a scratch along the seal diameter about 0.003 to 0.005 deep. Definately a leak path. I took a sanding tootsie roll and carefully worked this out, blending about half way around the diameter. Then polished the entire diameter. Re-assembled and pressure bled. 3 months later not a drop from anywhere. Pedal is good.
The bottom line is, in my estimation maybe DOT 5 is more prone to imperfections and sealing surfaces have to be very good. I was disappointed at the workmanship on the rebuilds, but maybe they would have been OK with DOT 3. Don't know.
I know the rebuilders don't like DOT 5 and maybe its due to the above. I do know that if you spill DOT 3 or if the rebuilt part leaks and damages an expensive paint job, will they reimburse you for the paint work? I think we all know the answer to that. It's just not worth the risk to me. If I had used DOT 3 and it leaked as the 5 did, I would be out thousands in paint repair to disamantle and pull the subframe to fix it. If you have a driver level car and you are not worried about having good paint, go for it and use DOT 3 (or 4 or 5.1).
I now categorize any rebuilt-restored part as an engine rebuild. Get good folks doing the work, but trust that no one did the job right. When assembling your engine, verify that all the machining was done correct and that all clearances are correct.
When I was contemplating using DOT 5 I read about every post I could find on the subject and it ran about 50-50 on folks that swear by it and folks that swear at it. Nothing absolutely definitive one way or the other.
FWIW here is the fluid I used:
https://www.amazon.com/dp/B002IAS82W?th=1
I'm not going to say it's the best out there, but it works for me. There are higher priced ones, but when you compare the MSDS's they all seem to be the same as the Johnsens.
Good luck.