Improvements to M600

Firmware/Marlin_main.cpp

@@ -3610,6 +3610,14 @@ static void gcode_M600(bool automatic, float x_position, float y_position, float
             plan_buffer_line_curposXYZE(FILAMENTCHANGE_EXFEED);
         }
 
+        //Retract filament to prevent drooling
+        if (!automatic)
+        {
+            current_position[E_AXIS] -= FILAMENTCHANGE_LOADRETRACT;
+            plan_buffer_line_curposXYZE(FILAMENTCHANGE_EFEED_FIRST);
+            st_synchronize();
+        }
+
         // Move XY back
         plan_buffer_line(lastpos[X_AXIS], lastpos[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], FILAMENTCHANGE_XYFEED);
         st_synchronize();
@@ -3618,6 +3626,14 @@ static void gcode_M600(bool automatic, float x_position, float y_position, float
         plan_buffer_line(lastpos[X_AXIS], lastpos[Y_AXIS], lastpos[Z_AXIS], current_position[E_AXIS], FILAMENTCHANGE_ZFEED);
         st_synchronize();
 
+        //Restore filament 
+        if (!automatic)
+        {
+            current_position[E_AXIS] += FILAMENTCHANGE_LOADRETRACT;
+            plan_buffer_line(lastpos[X_AXIS], lastpos[Y_AXIS], lastpos[Z_AXIS], current_position[E_AXIS], FILAMENTCHANGE_EFEED_FIRST, active_extruder);
+            st_synchronize();
+        }
+
         // Set E position to original
         plan_set_e_position(lastpos[E_AXIS]);