Why oh why would you want an OM-10 (or OM-30 aka OM-F))? Loaded with exposure problems, though you might not see all of them with negatives films wide exposure range. Look for an OM-1N, 2N. John
If you are going to consider any Olympus cameras, look at OM-1, OM-2, OM-3, or OM-4. Steer clear of the OM-10, or OM-F, they are entry lever junk, and have problems. The OM-G is an OM-10 with some of the bugs worked out, but still not decent enough quality to warrant spending any money on. If you want manual only, its OM-1 or 3, and auto modes any of the OM-2 versions, or OM-4.
I'm going to disagree with Rick on the OM-G (aka OM-20). I have 2 of them, and they are both capable and reliable. They are also a fair bit lighter than the single digit OM cameras. When I bought mine, they were incredibly cheap.
Avoid the OM-10.
An OM-2 (or 3, or 4) is definitely better than an OM-G, but not as likely to be as inexpensive. An OM-1 is also better, but you need a battery work-around.
If you get any of the OM bodies, it will be tough to resist the temptation to get more ... (I have an OM-1n, two OM-G, an OM-2s and an OM-2n).
I agree, the 300 did feel cheap and plasticky when I had one, but I loved it at the time. I prefer the OM-10.
So what's so wrong with the OM-10? Reading this thread had me pouring through OM2n auctions on Ebay... even though i don't actually need one. The OM10 is pretty small and light - it's even smaller than my Bessa R2a when put side by side.
I have an EOS100 that I got for free because every 30 or so shots for no apparent reason the shutter stays open for about a second,other than that and I can live with losing 1 shot per roll of film ,its a nice camera to use anmd gives fine results with all my EOS lenses