Considering a Speedmaster Day-Date model, Read this before you commit!
Levy03 in the TZ Omega Forum pointed out that there have been a trio of reports of Speedmaster Day-Date (Also known as Day-Date Month) models which have reportedly had the problem within warranty of failing to change the day of the week. In the first instance a purchaser of a 3523.30 had two examples fail from the same Authorized Dealer and was waiting on his third.
In the second instance a purchaser had to return his example (pictured above) to his dealer when the day wheel reportedly wasn't working properly.
It's hard to impossible to say if this is a fluke, a bad batch or a something more. However, it seems advisable to check any Day-Date-Month 7751 based chronograph for proper Day and Month changeover before you purchase it.
Here's what to do:
If both the day and month switch over smoothly between about 10pm and 2-3am then the watch is probably ok. If it doesn't... I would pick out another.
Thanks Levy for pointing this out.