High mileage maintenance

Here's the deal. I have a 89 honda accord. not original owner. Has 273,xxx miles+. I have been maintaining it to the best of my capabilities and with tried the least costly way(not really). ive done two tune ups in the past 12,000 miles and used high grade components. added new minor things : radiator hoses, fuel filter, spark plug wires, o2 sensors, anchor bushing, blah blah blah. Kept up with oil changes every 3,000 miles. Oil i use: 3qts of Castro gtx High Mileage formula 5-30w, with an "engine restorer & lubricant" additive by Automotive Products. Also use engine flush each oil change.

Now my question is: is there a better way i could be maintaining my car along with better use of Additives. My main concern is the oil i use. Ive been reading about other high mileage oils and i want to know which is best for me.

Some say synthetic you cant go wrong with. but i also heard that its more likely it'll leak if i switch to full synthetic since my engine has very high mileage.
so looking on to the many high mileage formulas out there. i cant figure which is the best: Valvoline Maxlife, Citgo Ultralife, O'Reily's, AMSOIL synthetic. I cant decide!

And does the grade matter 5-30, 10-30, 10-40w etc. I was recommended 5-30w but would it be better if i change to a diff grade?

Also, about cleaning. I've read about Auto-rx. what are your takes. I doubt seafoaming will do good to my car since it might clean too much.

Let me know anything you can think of to better maintain. Thanks!

Why the engine restore and lub every 3000 miles? You seem overly concerned with how clean the inside of your engine is. Is your engine burning lots of oil? Is your oil real dirty when you change it at 3000 miles? Are you having any trouble with oil fouling of your spark plugs? Is your driving mostly in town stop and go or very short trips so the engine never gets hot? Today's oil has the best additive packages to keep your engine clean that have ever been out there. I would think that changing your oil every 3000 miles is more than enough to keep your engine clean. Also synthetic oil changes every 3000 miles would get very expensive. I only have 190K and still use the oil change indicator that turns red every 7500 miles with no problems.
Jeff

well, im not "overly" concerned with how clean the engine is. i just want to keep it reliable and from blowing. I dont really use it as a stop and go type of transportation. I commute everyday. a week i commute about 200 miles. crazy i know..but i rarely use it for short distance trips. If i need to run errands locally, i usually take my cousins car when i can.

as far as the oil consumption. i have to add 1/4 quart each 1000 miles approx.
i would just appreciate any advice i can get to make my car more reliable. and if its an engine swap that's recommended. then ill look into it