Gram Display Cabinet not cooling

😕 Hi, newby to refrigeration, but experienced service engineer on commercial catering eqpt. Went to a Gram upright drinks chiller cabinet today, fault, not cooling. Unit runs r600a at 51 grams.
First problem was suction line giving 28psi. thinking the unit was possibly overcharged I released enough gas to bring the pressure down to 6psi. The problem I found then was that the cabinet temperature was slow to decrease and the condenser was uncomfortably hot to touch across its entire area, also despite cooling coming back on the suction line the compressor was over warm. The filter and the capillary were both hot. I suspect a blockage causing compressor overwork, but would greatly appreciate any informed thoughts. The customer purchased this bargain s/h from ebay at a cost of £400 just four months ago, so expects it to be perfect ?