My parts washer is from an automotive transmission shop. It didn't see abuse.  It features an oil absorbing clay bag and a side mounted filter.  I use a 5 micron filter.  With the filter and clay bag,  the solvent flow is clean and oil free and I can go years between changes.

The solvent I use is strictly Stoddard solvent or mineral spirits.  It's not harsh to paint or coatings, but I do keep it away from decals and soundproofing.  It's not as fast acting as brake cleaners, or chlorinated solvent; but safer and low evaporation.  A soft brush is also necessary.  I've read where a notable collector suggested carburetor dip or cleaner.  NOOOOO!  That stuff will dissolve anything it touches, so if your into looks, not a good idea to use.  For spot cleaning I like electrical rated solvent such as CRC's QD Electronic Cleaner. It's pretty safe for most plastics though it might be harsh on painted embossings on thumb levers and bails. I believe the ethanol in it is what helps, so I look for that as to their harshness or not.  I always have a few junk test pieces to try solvents on before I commit to something of value.

I did try the touch control, no noticeable difference in the "hammering"  feel.  I'm going to investigate "ring and cylinder", though it types good impressions.  Probably nothing there, but learn as I go.  The Royal 10 and HH both have hard platens, and yet the difference in touch is very noticeable between them.

Well I like the idea of being able to use the same solvent for years, so I may add a much smaller parts cleaning station to my shop. I only hesitated from buying one because I thought it would go through too much solvent - which isn't cheap when you buy it in those larger drums.

Regarding ring adjustment, I'd be very cautious. If you manually lift a type bar until it makes contact with the ring you should be able to just slide a piece of paper between the type slug and platen (kind of like checking the gap on a spark plug). If you can I would look at other things and leave the ring alone. 

I hear you loud and clear on the ring adjustment.  The thing I noticed on the segment is that there is some embossing in spots on the ring much more pronounced than on the much older model 10. It seems to be related to keys on or close to the home row.  I also checked the platen diameter.  It's about .007" to about .010" smaller than factory spec.  It shrunk?  According to the repair guide, that's the limit Royal recommends for getting the platen replaced or recovered.  Being that it is very hard, I will put it in the back lot until I have funds to have it recovered.  I hate to fix something that ain't broke.  Until then, it's still a riddle to solve as well.

Don't go too cheap on the solvent tank.  You'll want sturdiness that doesn't wobble or flex with 40 lbs. of machine in it.  A pump and filter goes a long way towards a satisfaction of having a clean machine and extended life of the solvent too.  I found mine on craigslist a 2 hour drive away.  It was worth the looking around at the new and used.

I never thought of looking for a used one, thanks for the suggestion. With regard to your platen, I wouldn't assume that the rubber shrunk. The factory spec size you mentioned could be for the standard platen, but there were also specialty platens available, even those made of brass or cork, which were used for allowing as many carbon copies as possible to be typed at once. Such slightly smaller diameter platens meant there was a larger gap between the type slug and rubber because the extra clearance was needed for all that extra paper and carbon sheets. It might be more telling to measure the existing clearance between the slug face and platen than to rely on some spec that might not apply to your specific HH.