The DG3804b 21j is a GMT movement by design, slow beat, and has become well respected for it's function and durability. When it's time for a full service you just remove it, hit it with a hammer and buy a brand spanking new one for $25 from Otto Frei or one of the other supply houses, with a guarantee. None of mine are noisy, but they are new from Frei and not from the factories that tend to be not so clean in their work. It might need a bit of lubricant.
I don't know of any ETA slow beat that is currently made, but the ETA 2846 is still available in NOS from some suppliers. Smith's Supply has them at a very good price, but they misused my credit card, so be careful with them. I converted an ETA 2846 to GMT, but the parts to convert are strictly Chinese, ETA never converted movements to GMT having only the ETA 2893-2 GMT in their line, and I was fortunate enough to have a few members here with extra parts I used.