I daydreamed about buying a lightly-used Omega Seamaster 300m Quartz with an Omega 1538 movement, and converting it to HAQ. It seems like a fantastic way to get a top quality watch at an attractive price, but I think I'm going to abandon the idea. Here's why.
The 1538 is the Omega branding of the ETA 255.461, which is not thermo-compensated, hence not high accuracy. But the electronic module for the 255.461 can be replaced by the module from the 255.561 or 255.563, both which are thermo-compensated. I've seen advice that says swapping the module is easy. What's more, the thermo-compensated modules can be regulated, so it should be possible to adjust the watch to excellent accuracy. There are many WUS threads describing this.
But I don't want to open the watch and do this myself. I got in touch with two watch service people, and each told me they wouldn't do the job. The first said he wasn't completely convinced the 1538 is certain to be compatible with the module from the 255.561 or 255.563, and I risk wasting my money. The second said that I'd end up with a Frankenstein hybrid that Omega and authorized repair centers, including his shop, would refuse to touch, even if all I need is new gaskets.
So, sadly, I think I'm going to give up. I like the Grand Seiko SBGX339, SBGX337, and especially the SBGX115, but those are a lot of money, and the SBGX115, which I like best of all, is fairly rare. It rubs me the wrong way that I could have a nice HAQ Seamaster for under $2,000.