Spawning units, deleting when player is far, and respawning when back

[jazzraill 3]

hi fellow modders

i'm working on a script that spawns units when player is near some kind of building, de-spawns when player is far and spawns again if player is near same kind of building again. here is my code :

_groups_nato = [];

x = true;

fn_find_base = 
	{
	_list = nearestObjects [player, _bases, 1000];
	_base = _list call bis_fnc_selectrandom;
	_return = getpos _base;
	_return
	};

fn_spawn_nato = 
	{
	if (count _groups_nato < 5) then 
		{
		_pos = [] call fn_find_base;
		_grp = creategroup west;
		for "_i" from 1 to 3 do {"B_Soldier_F" createUnit [_pos, _grp];};
		nul = [_grp, _pos] call BIS_fnc_taskdefend;
		_return = _grp;
		_return
		};
	};

while {x} do 
	{
	_grp = [] call fn_spawn_nato;
	_groups_nato = _groups_nato + [_grp];
	_ldr = leader _grp;
	if ((_ldr) distance player > 1000) then 
		{
		{deletevehicle _x} foreach units _grp;
		_groups_nato = _groups_nato - [_grp];
		};
	hint str _groups_nato;
	};

the spawning and de-spawning part of the script works, but it fails to spawn again when player is near same kind of buildings. any help will be appreciated.