leakage through flight computer

I did a leak test on my instruments and plumbing because I suspect my
ASI to be indicating low. I was surprised to find a rather large
leakage through the MNAV. I understand why the MNAV leaks, but would
welcome input from others on whether my observations are normal or not
before I open the instrument. Without the MNAV, the total pressure
line holds the pressure very well. If I include the MNAV, I am losing
total pressure at a rate of about 10knots/4sec (rough estimate, at
100knots). I didn’t add an additional capacity to the pressure line to
stabilize the pressure.

I do not need input on true vs. indicated airspeed. But I would
welcome input from others who have looked at such instrument leakages
as well.

Regards,

Thomas