Vintage 45 Lady with irregular time keeping - magnetized ? | Girard Perregaux

Vintage 45 Lady with irregular time keeping - magnetized ?

Hello forum,
I have just joined the forum and this is my first posting. My watch collection was started a few years back when I bought a Vintage 1945 Lady (ref. 2590). I have later accquired a Lady "F" (ref 8038), a Petit Chronographe (ref 8045) as well as Ferrari (ref 8025) all these watches run like smooth silk. However my first watch has not been running well at all. Shortly after I purchased it (from a local AD) it started losing time, but only when I was wearing it. If the watch was left sitting for days on the table, it kept the time very well (as well as can be expected from a mechanical watch of course). When worn it loses 15 minutes every hour, and therefore cannot be worn for timekeeping purposes! My AD opened the watch and couldn't find anything wrong and then suggested the watch was somehow being magnetized, but I sit (work) by my computer most of the day, and do not know of any magnetizing objects in the household. I have gone for simple walks in the park and it loses time like h... also in the park. Does anybody here have a clue as to what is wrong or what I can do do get closer to a solution to what causes the watch to misbehave so badly when worn. Thanks.