Brake/Servo Issue on 328

I have noticed recently that when I start her from cold after a few days lay up in the garage the brake peddle is rock hard (very little retardation) as I come off the drive but by the time I press the peddle again, say in 100 yds its perfect. I took her out yesterday and the same thing happened again except this time it carried on for at least 5 or 6 stomps on the peddle with very little retardation. The 7th time I hit peddle expecting no bite it was perfect with the resultant lock up of the fronts.

The car is an 87 328 with no ABS.

I have had this before on rally cars and it is usually associated with either a faulty servo or servo vacuum pipe. What I cannot understand here is why it only happens on initial start from cold. On all other occasions its perfect. Any ideas before I call the dealer.

I have posted this also on the technical section of the forum.

Thanks

Mark