UK Online was the only ISP I knew of who did SRA.
ADSL2+ pushing the line even harder is not going to help.
If you slow the connection down it might mean enough margin to cope, but if it is noise causing the disconnect (it might not be), then it must be pretty large through a line out of sync with those stats.
Lift and shift, moving the line to a different port at the exchange, in case it is a line port issue at the exchange end.
The customer can pay for a BT engineer visit £160 to £200 and risk them deciding the fault is customer side. So unless people are willing to try at the test socket to eliminate phones/wiring that is the way things stand.
I would also suggest that you try a different ADSL modem on the line. Some devices cope better with the combinations of exchange hardware and unique noise situation of each line. Or failing that see if any firmware updates are available for the modem.
To be brutually honest, you are seeing 3 resyncs on one day, i.e. offline for a minute or so, and one resync on another day. With ADSL based services this is not uncommon, it could be as simple as an electrically noisy vehicle passing now and then.
If a business cannot cope with 1 resync a day from their ADSL line then ADSL is not the product for them.
2hr SLA is interesting, as I thought the best that was possible from BT for ADSL was 4 to 8 hours for responding to line faults.