New 123 vacuum pump question

[Cr from Texas]

My original vacuum pump was weak and began making a mechanical knock noise. Based on the advice in other threads, I knew it was time to replace/rebuild. Since the noise was a mechanical knock, I opted to buy a new Pierburg (sp?) pump for about $300 from autohauzaz. The pump is marked as "Made in Spain" and comes with a new check valve. Installation was straight forward but took a long time because of the bottom two bolts.

The first change I noticed was I lost the ability to hold vacuum for a long period of time. With the original pump, I could unlock the doors the next day. With the new one, I loose the vacuum reserve and can not centrally unlock the doors after about 3 hours.

I got rid of the mechanical noise but I can now hear the pump valves working (a new sound for this car).

What could have happened since I only replaced the pump?
I'm wondering about the connection - was I supposed to put some kind of thread sealant on the line to check valve connection?
Has anyone had problems with this brand of pump?

Charles