Wow Dom, that's incredible amount of life from the o-ring on the tensioner. I'm betting that you removing it in checking valve clearances actually extended its life. When I replaced mine, it wasn't touched in almost 130K miles, the o-ring was visibly distorted when I removed it.
Bad-Dude - be careful when playing around with oil viscosity. Depends heavily on how the oil is being consumed. Thicker oil might slow down the oil consumption, as it naturally resists being burned off, but it has a side effect of clogging those oil drain holes even faster. Quite a few owners on other forums have resorted to running thicker oil to help slow consumption, only to have it suddenly start guzzling oil.
Another option is to try running a thinner oil and break up those deposits around the oil drain holes. Of course, this assumes that the holes are not completely clogged with deposits and that the cylinders are not too scuffed up. Some have gotten really good results with piston soaks to help break up those deposits - some having to run MMO or Kroil to help break those deposits up.
Same with oil additives - anything that is to added to the crankcase is hit or miss. Some have had luck with Lucas and MMO. Some swear by Auto-Rx, to which I actually had to tried out and see for myself ($26/bottle) - results were disappointing, found that it did squat. Engine deposits are too variable in composition - there are some that Auto-Rx will readily dissolve and some that it cannot. It will also swell up certain seals, depending on their composition - which is not unheard of for any solvent, but something to watch for in certain cases. Seems to work best if it stays in constant contact with the surface to be cleaned, but in an engine - much of the lubrication is splashed on components, which doesn't give this solvent much seat time to work.
Something like MMO (~$3-$4 a bottle) IMO, works as well if not better. I'd even use a flush over Auto-Rx - sure it would be very aggressive, but I'd also understand it better.