I noticed the last week or 2 my AC didn't seem to be working as well as it should. It would never get the thermostat down to below 74 and would run constantly. Even if I bumped it up a degree or 2 more it ran much longer than it used to.

The last couple of days when it would cut off I could hear what sounded like water dripping for a few seconds afterwards. Last night after running for hours I looked and saw a little water dripping out underneath the part (the coils?) in the basement and decided I needed someone to look at it so I shut it off.

About 10 hours later a service guy comes out, opens up the compartment with the coils and there is what appeared to me to be a lot of ice buildup - probably 1/3 to 1/2 covered and he points out a little rust. Then he goes outside to the compressor(?) and checks the pressure. He says it should be around 70 (although I don't recall if that was min or max) and shows me that it's leveling out around 40.

So, he says he can run a leak test, but he's pretty sure it's coming out of the coils that were iced over.
Or he can refill it with HCFC22 (6 pounds worth). He quotes me a price for full 6 pounds although I wonder if I'd need a full 6 pounds and he also says it will probably just leak out again.
So then he starts talking about replacing compressor and coils with their "Basic", "Silver" and "Platinum" options. The catch is, if I get the "Silver" or "Platinum" he says I'll also have to replace the furnace since those are 2-stage compressors which of course makes it even more expensive.

I know you can't give me a definitive authoritative answer especially without seeing it yourself, but I feel like I'm being pressured into buying a whole new AC and furnace when perhaps I could get by for another couple years with just refilling the coolant.

Other info: The filter was clean, water was flowing through the drain pipe despite some spilling onto the floor, system is about 9-10 years old. It's a Lennox.

The price of HCFC22 seemed high to me, but maybe it's just the going rate. Is it possible I would only need to top it off instead of buying 6 whole pounds of it?

What are the chances that if I filled it up now that it would just dissipate within the next month? By next spring?

I know the answer may be "it depends", but I'm just looking for any guidance since I'm clueless about this.

The only options offered to me were Amana and Goodman. I'm definitely going to get a 2nd opinion and shop around before I decide to spend thousands to replace the AC (and possibly furnace).

Sorry, I'm pretty clueless about this stuff. If more details might help, I can provide them. The ice melted fairly quickly once the cover was removed and I'm not running the AC until I figure out what I'm going to do.

The rust really doesn't look that bad to me, but I realize we're talking about a gas here and it might only take the smallest of pinholes for it to bleed the system dry.