I know one person who services their own AC. They invested in a vac pump and a couple of special gauges and a leak detector. The latter item is now fairly inexpensive.
There are good serviceable items available for not too many $$
see:
http://www.thetoolwarehouse.net/
My friend studied the subject like he flies his aircraft, taking notes and planning the steps thoroughly before attemptingto set out. You have to flush the whole system, that is an important step if your A/C has been contaminated or up to air for a long time. New compressors can crud up a system to the point it is full of "black death" from the Teflon blades in the compressor that turn to crud. Older compressors will not do this, so knowing exactly what you have is crutial. The choice of flushing additives is debatable, I believe he used Acetone at one point followed by somestuff that removes water. What oil to use is also something to be studied. There is too much on this subject for me to keep up with, I let an A/C shop do it. I dropped $1400 on new hoses, a new dryer, expansion valve and a recharge with R12. It still blows cold 3 or 4 years later so I am happy.
We don't have enough info to help you well.
Were your AC services based on definite leaks? Where were the leaks and were theygross leaks or minor leaks? What did the shop use for leak detectors, dye or sniffers? (Some say dye is corrosive).
Did the shop install new fittings on existing hoses, or new hoses and were they OE hoses or aftermarket hoses?
At the price of refrigerant gas there is no substitute for new hoses that should keep pressure for maybe another decade if the pump, expansion valve and so on are new.
Also, I suggest one avoid conversion to R134A unless that has already been done. Now, are up to this kind of job?