Wolfman, I am a 20 year HVAC Technician. Witht hat said, I will answer a few of your questions....
Once they fail, the system gets contaminated and you can never get it all out. He thinks that 2-3 years is common for a replacement compressor to last. Probably the leak in the A coil added additional strain and caused mine to fail early.
False... if you have a knowledgeable tech, he would know that they make a solution that cleans out the system, after a compressor blow out. I have used this "cleaner" many many times, in 20 years and have never had a compressor die after only 1 year of service. If cleaned properly, and a filter drier is put on the liquid and vapor lines, that compressor will last you as long as the original. My bet is, when the compressor was changed out, that is all that was done...a quickie change out.
Old system is 12 Seer. The new would be 13 Seer.
That is because the government has mandated that 13 seer is now the lowest rating a manufacture can make. 12 seer is no longer available.
So if I go up to a 15 seer unit, I don't have a quote yet, but I am speculating about $5500-$5800 based on what my neighbor paid for his Carrier(s). (he hastwo -2 1/2 ton systems in a two story house, I have one 3 ton system in a one story house. His were $5500 each.) Deduct $1500 for the tax credit and that would put me at about $4000 - $4300. For an extra $2 - $500, it would be worth moving up in the energy efficiency.
Carrier, Bryant, Lennox, Ruud, Goodman (Janitrol).... or any other brand, is just as good as the other. I have installed every brand known to man. They are all equal in the parts department. The difference is warranty, case design and how they were installed, to begin with.
Keep in mind.... MOST compressor failures are not due to the equipment, but due to lack of maintenance or power issues. The number one reason for compressor failures, that Ihave seen, is lack of maintenance by the home owner, or servicing company. Dirty evaporator coils and/or dirty condenser coils makes the top of my list. Next on the list would be power issues in the home...IE: frequent power surges or low power issues. Thermostats have also been an issue a few times. Some people have the old mercury round thermostats (T87) which have no time delay built in to them. Match that with an older system, with no time delay, and you have a disaster waiting to happen when the power surges.
Oh, if I go to the higher seer rating, and use the tax credit, then I can't use the tax credit on replacement windows, which this house really, really really, needs. So in most cases going to the higher rating would be a no-brainer. But if I do that, my windows, when I do them, if I do them next year will cost me $1500 more. (a bird in the hand is worth two in the bush comes to mind.)
Not so in Iowa...but Im not sure about Virgina. In Iowa, these 2 credits are completely separate of one another. We install HVAC equipment in new homes, which also have high eff. windows, insulation, water heaters and so on, and they still receive credit for each of these. Remember, there is a federal tax credit, and then there is also your local utility CASH REBATE, for installing high eff. HVAC, appliances, windows and so on.
Not only do you receive a tax credit, but you should also receive a cash rebate from your utility company. Keep in mind... most utility companies require you purchase AT LEAST a 14 SEER unit to qualify for the cash rebate. For the tax credit, it is calculated on the total installed cost...a percentage of it. Read more about the tax credit HERE
So now my opinion....
Repair or replace? If I had a reputable company that cleaned the system and installed filter driers, I would have no issues replacing. Your unit is 10 years old... life "expectancy" is about 15 years. Its not really a life expectancy, but more of an amount of time that the manufacture considers that the unit will remain at the efficiency it was rated at, when new.
Your 10 year old unit has probably dropped to a 11 or even 10 year seer, just from age.
If you plan to use the same company to replace the second compressor, I would opt for replacement. The one thing I would make damned sure of is that if they install a high efficiency A/C and furnace...I would assume it is both due to the price of the estimate, that they match the system. If not, rebates and tax credits will be denied and you will be left with a dead horse in a few years.
One other thing... the tax credit has a $1500 cap, over 2 years, I believe it is. You can claim 30% of the installed cost for the credit. So, that would be $1140 on a $3800 system.
REMEMBER this though... this is a tax credit!!! not a rebate. This is nothing more than a $1500 "right off" on your taxes...if you are self employed, this is a huge help. If you are an employee, with taxes being withheld for you... $1500 tax credit is not that big of a deal.
I hope I helped a little.... if you have more questions, Im happy to help.