$ cat memorycheck.awk
BEGIN { FS="\n"; RS="}\n"; ORS="}\n\n"; }

{
        for(X in D) delete D[X];

        for(N=2; N<=NF; N++)
        {
                split($N, A, "=");
                D[A[1]]=A[2];
        }
} D["service_description"]=="MEMORY_CHECK"

$ awk -f memorycheck.awk data

service {
host_name=sky.log.net
service_description=MEMORY_CHECK
modified_attributes=1
check_command=blah!blah!blah
check_period=24x7
notification_period=24x7
event_handler=
has_been_checked=1
check_execution_time=0.453
check_latency=1.701
check_type=0
current_state=2
last_state=2
last_hard_state=2
last_event_id=2522339
current_event_id=2523376
current_problem_id=1127556
last_problem_id=0
current_attempt=1
max_attempts=1
normal_check_interval=30.000000
retry_check_interval=2.000000
state_type=1
last_state_change=1335466482
last_hard_state_change=1335466482
last_time_ok=1334123115
last_time_warning=0
last_time_unknown=1335465427
last_time_critical=1336750629
plugin_output=CRITICAL:  Process was not found
long_plugin_output=
performance_data=
last_check=1336750629
next_check=1336752429
check_options=0
notified_on_unknown=1
notified_on_warning=0
notified_on_critical=1
current_notification_number=364
current_notification_id=2530346
last_notification=0
notifications_enabled=0
active_checks_enabled=1
passive_checks_enabled=1
event_handler_enabled=1
problem_has_been_acknowledged=0
acknowledgement_type=0
flap_detection_enabled=0
failure_prediction_enabled=1
process_performance_data=1
obsess_over_service=1
is_flapping=0
percent_state_change=0.00
check_flapping_recovery_notification=0
state_history=2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2
}

$