Clutch M Cylinder failure below 55*F??

[L DC]

The clutch master cylinder in my '87 VW QSW (JT code engine/drive train same as 4KQ) fails when ambient temperature fall below 55*F.

A bit of history regarding the matter since I have replaced the clutch master cylinder twice since mid 2006.

In 2006, the clutch pedal in my '87 QSW began to sink sporadically on the way to my brother's house and by the time I got there, some 55 miles away, it completely collapsed.

I replaced the clutch master cylinder and slave with "new" ones at a cost of about $130-$140 and $50-$60, respectively.

About a year later, in a cooler-than-normal ambient temperature for South Fl or 60*F, the clutch pedal sunk to the bottom as I put the car in reverse to back out of the driveway.

I immediately pulled the pedal with my foot and depressed it again to try to shift from reverse into first but nothing happened and car remained stuck in reverse. 

I shut engine off and tried pumping the clutch to see if I build hydraulic pressure to no avail.

I hopped into another car and headed for work.

Later that evening I get back in the QSW and everything worked as if nothing had happened, huh??.
Ambient temperature had risen to normal levels, above 85*F.

Over the next 3 or 4 months the car begins to experience slight clutch slippage sporadically when ambient temperatures are above 90*F combined with high humidity.

Finally, last summer and some 300 miles away from home, the clutch pedal sank to the bottom, yet again on a cool morning (about 55*F) and never returned back up on its own even after the weather warmed up. 

That time I just replaced the seals within the clutch master cylinder at a cost of some $21 and the clutch worked nicely. The Sporadic clutch slippage experienced on hot days mysteriously disappeared as well.

All was good until this week when the same symptoms began to manifest.

This time, 50*F in early morning, again the clutch pedal sinks to the bottom and I'm not able to shift as there's no apparent pressure in the master cylinder.

Once ambient temperature climbs to say 70*F or if I let the engine warm up some 15 minutes later, the clutch works fine.

I can only imagine the problem being exacerbated up north where temperature this time a year hit below 0* !!


Upon close inspection at the clutch master cylinder under the foot well, I noticed its accordion-like boot is wet with oil but not leaking.

The system was completely bled following each clutch master cylinder replacement.

So what gives??

Are the seals on the master cylinder prone to failure below a certain temperature and or moisture build up inside the cylinder? 

Could the brake fluid be the culprit, even though I'm using the one specified one?

Or could it be defective seals or scored clutch master cylinder wall?

I read a little passage on the possible culprit from SJM Autotechnik website where it describes moisture buildup on the master cylinder:

CLUTCH HYDRAULIC SYSTEM 
The Clutch Hydraulic system on the Audis is often overlooked during preventative maintenance. The fluid in the clutch hydraulic system comes from the brake master cylinder reservoir and should be replaced (flushed) on an annual basis. This "brake" fluid is hygroscopic and will absorb moisture over time. Flushing the brake system fluid will not get the fluid flushed out from the clutch master and slave cylinder. Over time this old fluid absorbs moisture which can cause failure of the master cylinder and slave cylinder due to corrosion and pitting of the internal cylinder surface. This pitting will cause the rubber cups on the piston to get cut and fail to hold pressure when pushing the clutch pedal in. This failure of the hydraulic system will cause the clutch pedal to go all the way to the floor and stay there.

http://www.sjmautotechnik.com/trouble_shooting/trans.html#clutch


Any BTDT?

Thanks for you valuable input as always.

-Regards,

Louis