Mac NOT automatically connecting to preferred wifi network

Question

Hi,
I am facing a problem with OS X 10.9.1 (Mavericks) wifi connection.
I use a Time Capsule as a base station and 13" Macbook Air (2012). The base station is connected to the internet through a PPOE connection.
Here are the details.
Since upgrading to OS X 10.9.1, my Mac automatically connects to preferred wifi network ONLY WHEN the wifi is available at start up or when the Mac wakes up from sleep, but NOT OTHERWISE. 
Before the upgrade, the Mac automatically connected to the preferred wifi network not just at start up, but whenever the wifi became available.
In other words, after the upgrade, if I boot up the Time Capsule base station and the Mac simultaneously, the Mac scans for the base station wifi network (this is configured as the top preferred wifi network) at start up, but since the base staion is still booting up, the Mac doesn't find the wifi. 
But once the base station has booted up and wifi is available, the Mac no longer bothers to join it.  At this point, the Mac is also not able to do Time Machine backups to the Time Capsule because it is not able to locate the Time capsule disk over the wifi.
This situation remains (i.e., the Mac being not connected to the wifi) unless I do ONE of the following:
1. I manually select the preferred wifi network using the wifi icon at the top of the screen;  OR
2. I put the Mac to sleep (by closing the cover) and then wake it up.  On wake up, it connects automatically to the preferred wifi network; OR
3. I turn of the wifi (using the wifi icon on the top) and turn it back on, at which point, the Mac automatically connects to the preferred wifi network.
I have tried everything possible including contacting Apple support, but so far the issue is unresolved. 
Appreciate any help you can provide.
Prem

Answer 1

I have had wireless problems intermittently for a year, and seriously for 6 weeks. Apple denied the issue and was no help in spite of many tens of thousands of people on their own discussions complaining. I found a post suggesting a couple of things which fixed the problem. I don't know if both are necessary, but the first by itself does not solve the problem.
Lock the channel of your router to channel 1, apparently Apple and 802.11n don't play well together on higher channels. When this becomes a standard this will be resolved I hope.
Open your network preferences, select 'airport' and advanced. Delete unused networks. Select your network.
Open TCP/IP and write down all the settings, configure iPv4 manually. Enter the settings manually. Turn off IpV6.
Open DNS and write down your DNS server. Delete it and re-enter it manually.
This has worked on 2 macbooks and an iMac for the last 3 weeks with no network drops.
Joe Shea
Philadelphia