Brake fluid loss mystery

[SuperRu]

Our daughters 95 Legacy Wagon 170k+

Twice this past winter during cold snaps the brake light came on and the brake fluid reservoir was low. Since then the fluid level has been stable. I’ve done the usual inspections and there is no evidence of leakage. No brake fluid under the drivers side carpet or any place else.
The only thing I can think of is when it is really cold outside the master cylinder is leaking into the brake booster and the fluid is being sucked into the engine.
Anyone have suggestions how to trouble shoot this?

 

[Hondaslayer]

You sure there is no leakage from the ABS pump? I have seen that leak on a few 95's / 96's

 

[eden]

have you traced out all lines and master cylinder while somebody was pumping the pedal?

 

[SuperRu]

You sure there is no leakage from the ABS pump? I have seen that leak on a few 95's / 96's

It doesn't show any obvious leakage there. Wouldn't the paint show some damage from leaking brake fluid? I'm going to clean up the engine compartment and keep an eye on it.

have you traced out all lines and master cylinder while somebody was pumping the pedal?

Yes I did try that. There is no fluid loss right now so it is hard to trouble shoot. I may just have to wait until it gets cold here again to find the source of the leak.

 

[eden]

have you checked the bleeding nuts are tight on the calipers?

 

[SuperRu]

Yes I did, when I pulled the wheels off. I will double check them though.